Keithley Keithley Instruments 6514 Manual

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Model 6514 System Electrometer

Instruction Manual

A GREATER MEASURE OF CONFIDENCE

Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176 - TestEquipmentDepot.com

WARRANTY

Keithley Instruments, Inc. warrants this product to be free from defects in material and w period of 1 year from date of shipment.

Keithley Instruments, Inc. warrants the following items for 90 days from the date of shipment: probes, cables, rechargeable batteries, diskettes, and documentation.

During the warranty period, we will, at our option, either repair or replace any product that proves to be defective.

To exercise this warranty, write or call your local Keithley representative, or contact Keithley headquarters in Cleveland, Ohio. You will be given prompt assistance and return instructions. Send the product, transportation prepaid, to the indicated service facility. Repairs will be made and the product returned, transportation prepaid. Repaired or replaced products are warranted for the balance of the original warranty period, or at least 90 days.

LIMIT A TION OF W

This warranty does not apply to defects resulting from product modification without Keithle consent, or misuse of any product or part. This warranty also does not apply to fuses, software, non-rechargeable batteries, damage from battery leakage, or problems arising from normal wear or failure to follow instructions.

THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. THE REMEDIES PROVIDED HEREIN ARE BUYER’S SOLE AND EXCLUSIVE REMEDIES.

NEITHER KEITHLEY INSTRUMENTS, INC. NOR ANY OF ITS EMPLOYEES SHALL BE LIABLE FOR ANY DIRECT, INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF ITS INSTRUMENTS AND SOFTWARE EVEN IF KEITHLEY INSTRUMENTS, INC., HAS BEEN ADVISED IN ADVANCE OF THE POSSIBILITY OF SUCH DAMAGES. SUCH EXCLUDED DAMAGES SHALL INCLUDE, BUT ARE NOT LIMITED TO: COSTS OF REMOVAL AND INSTALLATION, LOSSES SUSTAINED AS THE RESULT OF INJURY TO ANY PERSON, OR DAMAGE TO PROPERTY.

ARRANTY

orkmanship for a

y’s express written

A G R E A

T E R M E A S U R E O F C O N F I D E N C E

Keithley Instruments, Inc.

3/04

Model 6514 System Electrometer

Instruction Manual

Cleveland, Ohio, U.S.A.

Fourth Printing, May 2003

Document Number: 6514-901-01 Rev

. D

Manual Print History

The print history shown below lists the printing dates of all Revisions and Addenda created for this manual. The Revision Level letter increases alphabetically as the manual undergoes subsequent updates. Addenda, which are released between Revisions, contain important change information that the user should incorporate immediately into the manual. Addenda are numbered sequentially. When a new Revision is created, all Addenda associated with the previous Revision of the manual are incorporated into the new Revision of the manual. Each new Revision includes a revised copy of this print history page.

Revision A (Document Number 6514-901-01)

Addendum A (Document Number 6514-901-02).....................................................December 1998

Revision B (Document Number 6514-901-01) ........................................................ December 1998

Revision C (Document Number 6514-901-01) ................................................................. June 1999

Revision D (Document Number 6514-901-01)................................................................. May 2003

............................................................October 1998

All Keithley product names are trademarks or registered trademarks of Keithley Instruments, Inc. Other brand names are trademarks or registered trademarks of their respective holders.

afety Precautions

The following safety precautions should be observed before using this product and an some instruments and accessories would normally be used with non-hazardous voltages, there are situations where hazardous conditions may be present.

This product is intended for use by qualified personnel who recognize shock hazards and are familiar with the safety precautions required to avoid possible injury. Read and follow all installation, operation, and maintenance information carefully before using the product. Refer to the manual for complete product specifications

If the product is used in a manner not specified, the protection pr vided by the product may be impaired.

The types of product users are:

Responsible body is the individual or group responsible for the use and maintenance of equipment, for ensuring that the equip-

ment is operated within its specifications and operating limits, and for ensuring that operators are adequately trained

Operators use the product for its intended function. They must be trained in electrical safety procedures and proper use of the

instrument. They must be protected from electric shock and contact with hazardous live circuits.

Maintenance personnel perform routine procedures on the product to keep it operating properly, for example, setting the line

voltage or replacing consumable materials. Maintenance procedures are described in the manual. The procedures explicitly state if the operator may perform them. Otherwise, they should be performed only by service personnel.

Service personnel are trained to work on live circuits, and perform safe installations and repairs of products. Only properly

trained service personnel may perform installation and service procedures.

Keithley products are designed for use with electrical signals that are rated Measurement Category I and Measurement Category II, as described in the International Electrotechnical Commission (IEC) Standard IEC 60664. Most measurement, control, and data I/O signals are Measurement Category I and must not be directly connected to mains voltage or to voltage sources with high transient over-voltages. Measurement Category II connections require protection for high transient over-voltages often associated with local AC mains connections. Assume all measurement, control, and data I/O connections are for connection to Category I sources unless otherwise marked or described in the Manual.

Exercise extreme caution when a shock hazard is present. Lethal voltage may be present on cable connector jacks or test fixture . The American National Standards Institute (ANSI) states that a shock hazard exists when voltage levels greater than 30V RMS,

42.4V peak, or 60VDC are present. A good safety practice is to expect that hazardous voltage is present in any unknown

circuit before measuring.

Operators of this product must be protected from electric shock at all times. The responsible body must ensure that operators are prevented access and/or insulated from every connection point. In some cases, connections must be exposed to potential human contact. Product operators in these circumstances must be trained to protect themselves from the risk of electric shock.

If the circuit is capable of operating at or above 1000 volts, no conductive part of the circuit may be exposed.

Do not connect switching cards directly to unlimited power circuits. They are intended to be used with impedance limited sources. NEVER connect switching cards directly to AC mains. When connecting sources to switching cards, install protective devices to limit fault current and voltage to the card.

Before operating an instrument, make sure the line cord is connected to a properly grounded power receptacle. Inspect the connecting cables, test leads, and jumpers for possible wear, cracks, or breaks before each use.

When installing equipment where access to the main power cord is restricted, such as rack mounting, a separate main input power disconnect device must be provided, in close proximity to the equipment and within easy reach of the operator.

For maximum safety, do not touch the product, test cables, or any other instruments while power is applied to the circuit under test. ALWAYS remove power from the entire test system and discharge any capacitors before: connecting or disconnecting

y associated instrumentation. Although

5/03

cables or jumpers, installing or removing switching cards, or making internal changes, such as installing or removing jumpers.

Do not touch any object that could provide a current path to the common side of the circuit under test or power line (earth) ground. Always make measurements with dry hands while standing on a dry, insulated surface capable of withstanding the voltage being measured.

The instrument and accessories must be used in accordance with its specifications and operating instructions or the safety of the equipment may be impaired.

Do not exceed the maximum signal levels of the instruments and accessories, as defined in the specifications and operating information, and as shown on the instrument or test fixture panels, or switching card

When fuses are used in a product, replace with same type and rating for continued protection against fire hazard

Chassis connections must only be used as shield connections for measuring circuits, NOT as safety earth ground connections.

If you are using a test fixture, keep the lid closed while power is applied to the device under test. Safe operation requires the use of a lid interlock.

If a screw is present, connect it to safety earth ground using the wire recommended in the user documentation.

The symbol on an instrument indicates that the user should refer to the operating instructions located in the manual.

The symbol on an instrument shows that it can source or measure 1000 volts or more, including the combined effect of normal and common mode voltages. Use standard safety precautions to avoid personal contact with these voltages.

The symbol indicates a connection terminal to the equipment frame.

The

WARNING

information very carefully before performing the indicated procedure.

The

CAUTION

warranty.

Instrumentation and accessories shall not be connected to humans.

Before performing any maintenance, disconnect the line cord and all test cables.

To maintain protection from electric shock and fire, replacement components in mains circuits, including the power transformer, test leads, and input jacks, must be purchased from Keithley Instruments. Standard fuses, with applicable national safety approvals, may be used if the rating and type are the same. Other components that are not safety related may be purchased from other suppliers as long as they are equivalent to the original component. (Note that selected parts should be purchased only through Keithley Instruments to maintain accuracy and functionality of the product.) If you are unsure about the applicability of a replacement component, call a Keithley Instruments office for information

To clean an instrument, use a damp cloth or mild, water based cleaner. Clean the exterior of the instrument only. Do not apply cleaner directly to the instrument or allow liquids to enter or spill on the instrument. Products that consist of a circuit board with no case or chassis (e.g., data acquisition board for installation into a computer) should never require cleaning if handled according to instructions. If the board becomes contaminated and operation is affected, the board should be returned to the factory for proper cleaning/servicing.

heading in a manual explains dangers that might result in personal injury or death. Always read the associated

heading in a manual explains hazards that could damage the instrument. Such damage may invalidate the

1 Getting Started

General information ................................................................... 1-2

Warranty information .......................................................... 1-2

Contact information ............................................................ 1-2

Safety symbols and terms ................................................... 1-2

Inspection ............................................................................ 1-2

Options and accessories ...................................................... 1-3

System electrometer features ..................................................... 1-4

Front and rear panel familiarization ........................................... 1-5

Front panel summary .......................................................... 1-5

Rear panel summary ........................................................... 1-8

Power-up .................................................................................. 1-10

Line power connection ...................................................... 1-10

Line frequency selection ................................................... 1-10

Power-up sequence ........................................................... 1-11

Display ..................................................................................... 1-12

Status and error messages ................................................. 1-12

Default settings ......................................................................... 1-12

SCPI programming .................................................................. 1-15

2 Measurement Concepts

Measurement overview .............................................................. 2-2

Performance considerations ....................................................... 2-2

Warm-up period .................................................................. 2-2

Autozero .............................................................................. 2-2

Connection fundamentals ........................................................... 2-3

Input connector ................................................................... 2-3

Low noise input cables ........................................................ 2-5

Basic connections to DUT .................................................. 2-6

Test fixture .......................................................................... 2-9

Input protection ................................................................. 2-11

Floating measurements ..................................................... 2-11

Zero check and zero correct ..................................................... 2-13

Zero check ......................................................................... 2-13

Zero correct ....................................................................... 2-14

SCPI programming — zero check and zero correct ......... 2-15

Input bias current and offset voltage calibration ...................... 2-17

Front panel ........................................................................ 2-17

SCPI programming ........................................................... 2-18

Measurement considerations .................................................... 2-19

3Volts and Ohms Measurements

Measurement overview ............................................................... 3-2

Guarding ..................................................................................... 3-2

Test circuit leakage .............................................................. 3-2

Input cable leakage and capacitance ................................... 3-3

Volts and ohms measurement procedure .................................... 3-4

V-Drop and I-Source for ohms ............................................ 3-6

SCPI programming ..................................................................... 3-7

Programming example ........................................................ 3-8

Volts and ohms measurement considerations ............................. 3-9

Loading effects .................................................................... 3-9

Cable leakage resistance ...................................................... 3-9

Input capacitance (settling time) ....................................... 3-10

Guarding input cable ......................................................... 3-12

Application ............................................................................... 3-14

Capacitor dielectric absorption .......................................... 3-14

4 Amps Measurements

Measurement overview ............................................................... 4-2

Amps measurement procedure ................................................... 4-2

Damping .............................................................................. 4-4

High impedance measurement techniques ................................. 4-5

SCPI programming ..................................................................... 4-8

Programming example ........................................................ 4-9

Amps measurement considerations ............................................ 4-9

Input bias current ................................................................. 4-9

Voltage burden ..................................................................... 4-9

Noise .................................................................................. 4-10

Applications .............................................................................. 4-13

Diode leakage current ........................................................ 4-13

Capacitor leakage current .................................................. 4-14

Cable insulation resistance ................................................ 4-14

Surface insulation resistance (SIR) ................................... 4-15

5 Coulombs Measurements

Measurement overview ............................................................... 5-2

Auto discharge ............................................................................ 5-2

Coulombs measurement procedure ............................................ 5-3

SCPI programming ..................................................................... 5-5

Programming example ........................................................ 5-6

Coulombs measurement considerations ..................................... 5-6

Input bias current ................................................................. 5-6

External voltage source ....................................................... 5-6

Zero check hop and auto discharge hop .............................. 5-7

Application ................................................................................. 5-7

Capacitance measurements ................................................. 5-7

6 Range, Units, Digits, Rate, and Filters

Range, units, and digits .............................................................. 6-2

Range .................................................................................. 6-2

Units .................................................................................... 6-4

Digits ................................................................................... 6-4

SCPI programming - range and digits ................................ 6-4

Rate ............................................................................................ 6-6

SCPI programming — rate ................................................. 6-7

Filters ......................................................................................... 6-8

Median filter ........................................................................ 6-8

Digital filter ......................................................................... 6-9

SCPI programming — filters ............................................ 6-10

7 Relative, mX+b and Percent (%)

Relative ....................................................................................... 7-2

Setting and controlling relative ........................................... 7-2

SCPI programming — relative ........................................... 7-3

mX+b and percent (%) ............................................................... 7-4

mX+b .................................................................................. 7-4

Percent (%) .......................................................................... 7-5

SCPI programming — mX+b and percent ......................... 7-6

8 Buffer

Buffer operations ........................................................................ 8-2

Store .................................................................................... 8-2

Recall .................................................................................. 8-2

Buffer statistics ................................................................... 8-3

SCPI programming .................................................................... 8-4

Programming example......................................................... 8-6

9Triggering

Trigger models ........................................................................... 9-2

Idle and initiate ................................................................... 9-4

Trigger model operation ...................................................... 9-4

Trigger model configuration — front panel ........................ 9-7

SCPI programming ..................................................................... 9-9

Programming example ...................................................... 9-10

External triggering ................................................................... 9-11

Input trigger requirements ................................................. 9-11

Output trigger specifications ............................................. 9-12

External trigger example ................................................... 9-12

10 Limit T ests

Limit testing .............................................................................. 10-2

Binning ..................................................................................... 10-4

Component handler interface ............................................ 10-6

Component handler types .................................................. 10-7

Digital output clear pattern ................................................ 10-8

Front panel operation .............................................................. 10-10

Limit test configuration ................................................... 10-10

Perform limit tests ........................................................... 10-11

SCPI programming ................................................................. 10-12

Programming example .................................................... 10-15

11 Digital I/O, Analog Outputs, and External Feedback

Digital I/O port ......................................................................... 11-2

Sink mode — controlling external devices ....................... 11-3

Source mode — logic control ............................................ 11-5

Setting digital output lines ................................................. 11-5

SCPI programming — digital output pattern .................... 11-6

Analog outputs .......................................................................... 11-7

2V analog output ............................................................... 11-7

External feedback ................................................................... 11-11

Electrometer input circuitry ............................................ 11-11

Shielded fixture construction ........................................... 11-12

Non-standard coulombs ranges ....................................... 11-13

External feedback procedure ........................................... 11-13

Logarithmic currents ....................................................... 11-15

Non-decade current gains ................................................ 11-16

SCPI programming — external feedback ....................... 11-17

12 Remote Operation

Selecting and configuring an inter ace ..................................... 12-2

Interfaces ........................................................................... 12-2

Languages .......................................................................... 12-2

Interface selection and configuration procedures .............. 12-2

GPIB operation and reference .................................................. 12-5

GPIB bus standards ........................................................... 12-5

GPIB bus connections ....................................................... 12-5

Primary address selection .................................................. 12-7

General bus commands ..................................................... 12-8

Front panel GPIB operation ............................................ 12-10

Programming syntax ....................................................... 12-11

RS-232 interface reference ..................................................... 12-17

Sending and receiving data .............................................. 12-17

RS-232 settings ............................................................... 12-17

RS-232 connections ......................................................... 12-18

Error messages ................................................................ 12-19

13 Status Structure

Overview .................................................................................. 13-2

Clearing registers and queues ................................................... 13-4

Programming and reading registers ......................................... 13-5

Programming enable registers ........................................... 13-5

Reading registers ............................................................... 13-6

Status byte and service request (SRQ) ..................................... 13-7

Status byte register ............................................................ 13-7

Service request enable register .......................................... 13-8

Serial polling and SRQ ..................................................... 13-9

Status byte and service request commands ....................... 13-9

Status register sets .................................................................. 13-11

Condition registers .......................................................... 13-15

Event registers ................................................................. 13-16

Event enable registers ..................................................... 13-17

Queues .................................................................................... 13-18

Output queue ................................................................... 13-18

Error queue ...................................................................... 13-19

14 Common Commands 15 SCPI Signal Oriented Measurement Commands 16 DISPlay , FORMat, and SYSTem

DISPlay subsystem .................................................................. 16-2

FORMat subsystem .................................................................. 16-4

SYSTem subsystem .................................................................. 16-8

17 SCPI Reference T ables

General notes ............................................................................ 17-2

18 Performance V eriﬁcation

Introduction .............................................................................. 18-2

Verification test requirements ................................................... 18-3

Environmental conditions ................................................. 18-3

Warm-up period ................................................................ 18-3

Line power ........................................................................ 18-3

Recommended test equipment ................................................. 18-4

Verification limits ..................................................................... 18-6

Example reading limits calculation ................................... 18-6

Recalculating resistance reading limits ............................. 18-6

Calibrator voltage calculations ................................................. 18-7

Current calculations .......................................................... 18-7

Charge calculations ........................................................... 18-7

Performing the verification test procedures .............................. 18-8

Test summary .................................................................... 18-8

Test considerations ............................................................ 18-8

Restoring factory defaults ......................................................... 18-9

Input bias current and offset voltage calibration ...................... 18-9

Offset voltage calibration .................................................. 18-9

Input bias current calibration ............................................. 18-9

Volts measurement accuracy .................................................. 18-10

Amps measurement accuracy ................................................. 18-12

20µA-20mA range accuracy ........................................... 18-12

20pA-2µA range accuracy .............................................. 18-13

Ohms measurement accuracy ................................................. 18-15

Ω

-20MΩ range accuracy ............................................. 18-15

200MΩ-200GΩ range accuracy ...................................... 18-17

Coulombs measurement accuracy .......................................... 18-18

19 Calibration

Introduction .............................................................................. 19-2

Environmental conditions ......................................................... 19-2

Temperature and relative humidity..................................... 19-2

Warm-up period ................................................................. 19-2

Line power ......................................................................... 19-2

Calibration considerations ........................................................ 19-3

Calibration cycle ................................................................ 19-3

Recommended calibration equipment ...................................... 19-3

Calibration errors ...................................................................... 19-5

Calibration menu ...................................................................... 19-5

Aborting calibration .................................................................. 19-5

Current and charge calculations ............................................... 19-6

Manual calculations............................................................ 19-6

Automatic calculations ...................................................... 19-6

Calibration procedure ............................................................... 19-7

Preparing for calibration .................................................... 19-7

Input bias current and offset voltage calibration ............... 19-7

Volts calibration ................................................................. 19-8

Amps calibration ............................................................. 19-10

Coulombs calibration ...................................................... 19-14

Ohms calibration ............................................................. 19-16

Entering calibration dates and saving calibration ............ 19-18

Locking out calibration ................................................... 19-18

Changing the calibration code ................................................ 19-18

Resetting the calibration code ................................................ 19-19

Displaying calibration dates ................................................... 19-19

Displaying the calibration count ............................................. 19-20

20 Routine Maintenance

Introduction .............................................................................. 20-2

Setting line voltage and replacing line fuse ............................. 20-2

Front panel tests ................................................................ 20-4

DISP test ........................................................................... 20-4

KEY test ............................................................................ 20-4

A Speciﬁcations B Status and Error Messages C General Measurement Considerations

Measurement considerations ..................................................... C-2

Ground loops ...................................................................... C-2

Triboelectric effects ........................................................... C-3

Piezoelectric and stored charge effects .............................. C-3

Electrochemical effects ...................................................... C-4

Humidity ............................................................................ C-4

Light ................................................................................... C-4

Electrostatic interference ................................................... C-4

Magnetic fields ................................................................... C-5

Electromagnetic Interference (EMI) .................................. C-5

D DDC Emulation Commands

DDC language ........................................................................... D-2

E Example Programs

Programming examples .............................................................. E-2

Changing function and range .............................................. E-2

One-shot triggering ............................................................. E-3

Generating SRQ on buffer full ............................................ E-4

Storing readings in buffer ................................................... E-5

Taking readings using the :READ? command .................... E-6

Controlling the Model 6514 via the RS-232 COM2 port ... E-7

F IEEE-488 Bus Overview

Introduction ............................................................................... F-2

Bus description .......................................................................... F-3

Bus lines .................................................................................... F-5

Data lines ............................................................................ F-5

Bus management lines ........................................................ F-5

Handshake lines .................................................................. F-6

Bus commands ........................................................................... F-7

Uniline commands .............................................................. F-8

Universal multiline commands ........................................... F-8

Addressed multiline commands ......................................... F-9

Address commands ............................................................ F-9

Unaddress commands ......................................................... F-9

Common commands ......................................................... F-10

SCPI commands ............................................................... F-10

Command codes ............................................................... F-10

Typical command sequences ............................................ F-11

IEEE command groups ..................................................... F-12

Interface function codes .......................................................... F-13

G IEEE-488 and SCPI Conformance Information

Introduction ............................................................................... G-2

H Calibration Options

Introduction ............................................................................... H-2

Reading calibration standard values .......................................... H-2

Data transfer connections ................................................... H-2

Reading values ................................................................... H-2

Example program ............................................................... H-3

Remote calibration ..................................................................... H-4

Calibration commands ........................................................ H-4

Remote calibration overview .............................................. H-4

List of Illustrations

1 Getting Started

Figure 1-1 Model 6514 front panel .......................................................... 1-5

Figure 1-2 Model 6514 rear panel ........................................................... 1-8

2 Measurement Concepts

Figure 2-1 Input connector configurations .............................................. 2-4

Figure 2-2 Maximum input levels ........................................................... 2-5

Figure 2-3 Basic connections for unguarded measurements ................... 2-6

Figure 2-4 Shielding for unguarded measurements ................................. 2-7

Figure 2-5 Basic connections for guarded measurements ....................... 2-8

Figure 2-6 General purpose test fixture ................................................... 2-9

Figure 2-7 Capacitor test circuit without protection .............................. 2-11

Figure 2-8 Capacitor test circuit with protection ................................... 2-11

Figure 2-9 Floating measurements ........................................................ 2-12

Figure 2-10 Equivalent input impedance with zero check enabled ......... 2-14

3Volts and Ohms Measurements

Figure 3-1 High-impedance voltage measurements ................................ 3-3

Figure 3-2 Connections for unguarded volts and ohms ........................... 3-5

Figure 3-3 Connections for guarded volts and ohms ............................... 3-6

Figure 3-4 Meter loading ......................................................................... 3-9

Figure 3-5 Effects of input capacitance ................................................. 3-11

Figure 3-6 Settling time ......................................................................... 3-12

Figure 3-7 Unguarded input cable ......................................................... 3-12

Figure 3-8 Guarded input cable ............................................................. 3-13

Figure 3-9 Measuring dielectric absorption ........................................... 3-15

4 Amps Measurements

Figure 4-1 Connections for amps ............................................................ 4-4

Figure 4-2 High impedance current measurements ................................. 4-5

Figure 4-3 Floating current measurements .............................................. 4-7

Figure 4-4 Voltage burden considerations ............................................. 4-10

Figure 4-5 Source resistance and capacitance ....................................... 4-11

Figure 4-6 Connections; diode leakage current test .............................. 4-13

Figure 4-7 Connections; capacitor leakage current test ......................... 4-14

Figure 4-8 Connections; cable insulation resistance test ....................... 4-14

Figure 4-9 Connections; surface insulation resistance test .................... 4-15

5 Coulombs Measurements

Figure 5-1 Typical connections for coulombs .......................................... 5-4

Figure 5-2 Measuring capacitors ............................................................. 5-7

6 Range, Units, Digits, Rate, and Filters

Figure 6-1 Speed vs. noise characteristics ............................................... 6-6

Figure 6-2 Digital filter types; m ving and repeating .............................. 6-9

8 Buffer

Figure 8-1 Buffer locations ...................................................................... 8-3

9Triggering

Figure 9-1 Trigger model — front panel operation ................................. 9-2

Figure 9-2 Trigger model — remote operation ........................................ 9-3

Figure 9-3 Measure action block of trigger model .................................. 9-6

Figure 9-4 Trigger link connection operation ........................................ 9-11

Figure 9-5 Trigger link input pulse specifications ................................. 9-11

Figure 9-6 Trigger link output pulse specifications ............................... 9-12

Figure 9-7 DUT test system ................................................................... 9-12

Figure 9-8 Trigger link connections ....................................................... 9-13

Figure 9-9 Operation model for triggering example .............................. 9-14

10 Limit T ests

Figure 10-1 Limit tests ............................................................................. 10-2

Figure 10-2 Limit tests example .............................................................. 10-2

Figure 10-3 Operation model for limit test .............................................. 10-3

Figure 10-4 Binning system ..................................................................... 10-4

Figure 10-5 Operation model for limit testing with binning .................... 10-5

Figure 10-6 Handler interface connections .............................................. 10-6

Figure 10-7 Digital output auto-clear timing example ............................. 10-9

11 Digital I/O, Analog Outputs, and External Feedback

Figure 11-1 Digital I/O port ..................................................................... 11-2

Figure 11-2 Digital I/O port simplified schematic ................................... 11-3

Figure 11-3 Controlling externally powered relays ................................. 11-4

Figure 11-4 NAND gate control .............................................................. 11-5

Figure 11-5 Typical 2V analog output connections ................................. 11-8

Figure 11-6 Typical preamp out connections ........................................... 11-9

Figure 11-7 Electrometer input circuitry (external feedback mode) ...... 11-12

Figure 11-8 Shielded fixture construction .............................................. 11-14

Figure 11-9 “Transdiode” logarithmic current configuration ................ 11-15

Figure 11-10 Non-decade current gains ................................................... 11-16

12 Remote Operation

Figure 12-1 IEEE-488 connector ............................................................. 12-5

Figure 12-2 IEEE-488 connections ......................................................... 12-6

Figure 12-3 IEEE-488 connector location ............................................... 12-7

Figure 12-4 RS-232 interface connector ............................................... 12-18

13 Status Structure

Figure 13-1 6514 status mode structure .................................................. 13-3

Figure 13-2 16-bit status register ............................................................. 13-6

Figure 13-3 Status byte and service request ............................................ 13-7

Figure 13-4 Standard event status .......................................................... 13-12

Figure 13-5 Operation event status ........................................................ 13-13

Figure 13-6 Measurement event status .................................................. 13-14

Figure 13-7 Questionable event status ................................................... 13-15

16 DISPlay , FORMat, and SYSTem

Figure 16-1 ASCII data format ................................................................ 16-5

Figure 16-2 IEEE-754 single precision data format (32 data bits) .......... 16-5

Figure 16-3 Key-press codes ................................................................. 16-10

18 Performance V eriﬁcation

Figure 18-1 Connections for volts verification ...................................... 18-10

Figure 18-2 Connections for 20µA-20mA range verification ............... 18-12

Figure 18-3 Connections for 20pA-20µA range verification ................ 18-13

Ω

Figure 18-4 Connections for ohms verification (2 Figure 18-5 Connections for ohms verification

(200MΩ-200GΩ ranges) .............................................. 18-17

Figure 18-6 Connections for coulombs verification .............................. 18-18

-20MΩ ranges) ... 18-15

19 Calibration

Figure 19-1 Connections for volts calibration ......................................... 19-8

Figure 19-2 Connections for 20µA-20mA range calibration ................ 19-10

Figure 19-3 Connections for 20pA-2mA range calibration ................... 19-11

Figure 19-4 Connections for coulombs calibration ............................... 19-14

Figure 19-5 Connections for ohms calibration

Ω

and 2MΩ ranges) ................................................ 19-16

(2k

Figure 19-6 Connections for ohms calibration (2GΩ range) ................ 19-17

20 Routine Maintenance

Figure 20-1 Power module ...................................................................... 20-3

C General Measurement Considerations

Figure C-1 Power line ground loops ........................................................ C-2

Figure C-2 Eliminating ground loops ...................................................... C-3

F IEEE-488 Bus Overview

Figure F-1 IEEE-488 bus configuration .................................................. F-4

Figure F-2 IEEE-488 handshake sequence ............................................. F-6

Figure F-3 Command codes .................................................................... F-8

H Calibration Options

Figure H-1 Data transfer connections ...................................................... H-2

List of T ables

1 Getting Started

Table 1-1 SCPI commands - line frequency ........................................ 1-10

Table 1-2 Default settings .................................................................... 1-13

2 Measurement Concepts

Table 2-1 Basic measurement capabilities ............................................. 2-2

Table 2-2 SCPI commands — autozero ................................................. 2-3

Table 2-3 Display messages for zero check and zero correct .............. 2-13

Table 2-4 SCPI commands — zero check and zero correct ................. 2-15

Table 2-5 SCPI commands — input bias current and offset

Table 2-6 Summary of measurement considerations ........................... 2-19

3Volts and Ohms Measurements

Table 3-1 SCPI commands — volts and ohms function ........................ 3-7

4 Amps Measurements

Table 4-1 SCPI commands — amps function ........................................ 4-8

Table 4-2 Minimum recommended source resistance values .............. 4-11

5 Coulombs Measurements

Table 5-1 SCPI commands — coulombs function ................................. 5-5

voltage calibration .......................................................... 2-18

6 Range, Units, Digits, Rate, and Filters

Table 6-1 Measurement ranges .............................................................. 6-2

Table 6-2 SCPI commands — range and digits ..................................... 6-4

Table 6-3 SCPI commands — rate ......................................................... 6-7

Table 6-4 SCPI commands — filters ................................................... 6-10

7 Relative, mX+b and Percent (%)

Table 7-1 Range symbols for rel values ................................................. 7-3

Table 7-2 SCPI commands — relative (null) ......................................... 7-3

Table 7-3 SCPI commands — mX+b and percent ................................. 7-6

8 Buffer

Table 8-1 SCPI commands — buffer ..................................................... 8-4

9Triggering

Table 9-1 Auto delay settings ................................................................. 9-6

Table 9-2 SCPI commands — triggering ............................................... 9-9

10 Limit T ests

Table 10-1 Test limit display messages .................................................. 10-3

Table 10-2 SCPI commands — limit tests ........................................... 10-12

11 Digital I/O, Analog Outputs, and External Feedback

Table 11-1 SCPI commands — digital outputs ...................................... 11-6

Table 11-2 Example 2V analog output values ........................................ 11-7

Table 11-3 Full-range preamp out values ............................................. 11-10

Table 11-4 SCPI commands — external feedback ............................... 11-17

12 Remote Operation

Table 12-1 General bus commands ........................................................ 12-8

Table 12-2 PC serial port pinout ........................................................... 12-19

Table 12-3 RS-232 connector pinout .................................................... 12-19

13 Status Structure

Table 13-1 Common and SCPI commands — reset registers and

clear queues .................................................................... 13-4

Table 13-2 SCPI command — data formats for reading

status registers ................................................................ 13-6

Table 13-3 Common commands — status byte and service request

enable registers ............................................................... 13-9

Table 13-4 Common and SCPI commands — condition registers ....... 13-16

Table 13-5 Common and SCPI commands — event registers ............. 13-16

Table 13-6 Common and SCPI commands — event enable

registers ......................................................................... 13-17

Table 13-7 SCPI commands — error queue ......................................... 13-20

14 Common Commands

Table 14-1 IEEE-488.2 common commands and queries ...................... 14-2

15 SCPI Signal Oriented Measurement Commands

Table 15-1 Signal oriented measurement command summary .............. 15-2

16 DISPlay , FORMat, and SYSTem

Table 16-1 SCPI commands — display ................................................. 16-2

Table 16-2 SCPI commands — data format ........................................... 16-4

Table 16-3 SCPI commands — system .................................................. 16-8

17 SCPI Reference T ables

Table 17-1 CALCulate command summary .......................................... 17-2

Table 17-2 FORMat command summary ............................................... 17-5

Table 17-3 DISPlay command summary ............................................... 17-5

Table 17-4 SENSe command summary ................................................. 17-6

Table 17-5 STATus command summary ................................................ 17-9

Table 17-6 SOURce command summary ............................................... 17-9

Table 17-7 SYSTem command summary ............................................ 17-11

Table 17-8 TRACe command summary .............................................. 17-12

Table 17-9 TRIGger command summary ............................................ 17-13

18 Performance V eriﬁcation

Table 18-1 Recommended verification equipment ................................ 18-4

Table 18-2 Voltage measurement accuracy reading limits ................... 18-11

Table 18-3 20mA-20mA range current measurement accuracy

reading limits ................................................................ 18-13

Table 18-4 20pA-2µA range current measurement accuracy

reading limits ................................................................ 18-14

Ω

Table 18-5 2k

Table 18-6 200MΩ-200GΩ resistance measurement

Table 18-7 Coulombs measurement accuracy reading limits .............. 18-19

-20MΩ range resistance measurement

accuracy limits ............................................................. 18-16

accuracy limits ............................................................. 18-17

19 Calibration

Table 19-1 Recommended calibration equipment ................................. 19-4

Table 19-2 Calibration menu ................................................................. 19-5

Table 19-3 Volts calibration summary ................................................... 19-9

Table 19-4 20mA-20mA range amps calibration summary ................. 19-11

Table 19-5 20pA-2µA range amps calibration summary ..................... 19-13

Table 19-6 Coulombs calibration summary ......................................... 19-15

Table 19-7 Ohms calibration summary ................................................ 19-17

20 Routine Maintenance

Table 20-1 Power line fuse ..................................................................... 20-3

Table 20-2 Front panel tests ................................................................... 20-4

B Status and Error Messages

Table B-1 Status and error messages ..................................................... B-2

D DDC Emulation Commands

Table D-1 Device dependent command summary ................................. D-2

F IEEE-488 Bus Overview

Table F-1 IEEE-488 bus command summary ........................................ F-7

Table F-2 Hexadecimal and decimal command codes ........................ F-10

Table F-3 Typical bus sequence ........................................................... F-11

Table F-4 Typical addressed command sequence ................................ F-11

Table F-5 IEEE command groups ....................................................... F-12

Table F-6 Model 6514 interface function codes .................................. F-13

G IEEE-488 and SCPI Conformance Information

Table G-1 IEEE-488 documentation requirements ................................ G-2

Table G-2 Coupled commands ............................................................... G-4

H Calibration Options

Table H-1 Calibration commands .......................................................... H-4

Getting Started

•

General information

tion, contact information, safety symbols and terms, inspection, and available options and accessories.

•

System electrometer features

— Covers general information that includes warranty informa-

— Summarizes the features of Model 6514.

Front and rear panel familiarization

• instrument.

•

Power-up

power line frequency, and the power-up sequence.

•

Display Default settings

• three user def ned, GPIB defaults, or factory defaults.

•

SCPI programming

— Covers line power connection, line voltage setting, fuse replacement,

— Provides information about the display of Model 6514.

— Covers the fi e instrument setup conf gurations available to the user;

— Explains how SCPI commands are presented in this manual.

— Summarizes the controls and connectors of the

1-2 Getting Started

General information

Warranty information

Warranty information is located at the front of this manual. Should your Model 6514 require warranty service, contact the Keithley representative or authorized repair facility in your area for further information. When returning the instrument for repair, be sure to f ll out and include the service form at the back of this manual to provide the repair facility with the necessary information.

Contact information

Worldwide phone numbers are listed at the front of this manual. If you have any questions, please contact your local Keithley representative or call one of our Application Engineers at 1-800-348-3735 (U.S. and Canada only).

Safety symbols and terms

The following symbols and terms may be found on the instrument or used in this manual:

The symbol on an instrument indicates that the user should refer to the operating instructions located in the manual.

The symbol on the instrument shows that high voltage may be present on the terminal(s). Use standard safety precautions to avoid personal contact with these voltages.

The

WARNING

injury or death. Always read the associated information very carefully before performing the indicated procedure.

The

CAUTION

ment. Such damage may invalidate the warranty.

heading used in this manual explains dangers that might result in personal

heading used in this manual explains hazards that could damage the instru-

Inspection

Model 6514 was carefully inspected electrically and mechanically before shipment. After unpacking all items from the shipping carton, check for any obvious signs of physical damage that may have occurred during transit. (There may be a protective film ver the display lens, which can be removed). Report any damage to the shipping agent immediately. Save the original packing carton for possible future shipment. The following items are included with every Model 6514 order:

• Model 6514 System Electrometer with line cord.

• Model 237-ALG-2 triax cable.

• Accessories as ordered.

• Certificate of calibration.

• Model 6514 Instruction Manual (P/N 6514-901-01).

• Manual Addenda (pertains to any improvements or changes concerning the instrument

If an additional manual is required, order the appropriate manual package. The manual packages include a manual and any pertinent addenda.

or manual).

Options and accessories

Input cables, connectors and adapters

Model 237-ALG-2 — This is a 6.6 ft (2-meter) low-noise triax cable terminated with a 3-slot

male triax connector on one end and 3 alligator clips on the other. (One Model 237-ALG-2 is included).

Model 237-BNC-TRX adapter — This is a male BNC to 3-lug female triax connector

(guard disconnected). It is used to terminate a triax cable with a BNC plug.

Model 237-TRX-T adapter — This is a 3-slot male to dual 3-lug female triax tee adapter for

use with 7078-TRX triax cables.

Model 237-TRX-TBC connector — This is a 3-lug female triax bulkhead (internal mount)

connector with cap for assembly of custom test f xtures and interface connections.

Model 7078-TRX-TBC connector — This is a 3-lug female triax bulkhead (external mount)

connector with cap for assembly of custom test f xtures and interface connections.

Model 7078-TRX-3, 7078-TRX-10 and Models 7078-TRX-20 triax cables — These are

low noise triax cables terminated at both ends with 3-slot male triax connectors. The -3 model is 3 ft (0.9m) in length, the -10 model is 10 ft (3m) in length, and the -20 model is 20 ft (6m) in length.

Getting Started 1-3

CS-751 barrel adapter — This is a barrel adapter that allows you to connect two triax cables

together. Both ends of the adapter are terminated with 3-lug female triax connectors.

GPIB and trigger link cables and adapters

Models 7007-1 and 7007-2 shielded GPIB cables — Connect Model 6514 to the GPIB bus

using shielded cables and connectors to reduce electromagnetic interference (EMI). Model 7007-1 is lm long; Model 7007-2 is 2m long.

Models 8501-1 and 8501-2 trigger link cables — Connect Model 6514 to other instruments

with Trigger Link connectors (e.g., Model 7001 Switch System). Model 8501-1 is lm long; Model 8501-2 is 2m long.

Model 8502 trigger link adapter — Lets you connect any of the six trigger link lines of

Model 6514 to instruments that use the standard BNC trigger connectors.

Model 8503 DIN to BNC trigger cable — Lets you connect trigger link lines one (Voltmeter

Complete) and two (External Trigger) of Model 6514 to instruments that use BNC trigger connectors. Model 8503 is lm long.

1-4 Getting Started

Rack mount kits

Model 4288-1 single ﬁxed rack mount kit — Mounts a single Model 6514 in a standard

19-inch rack.

Model 4288-2 side-by-side rack mount kit — Mounts two instruments (Models 182, 428,

486, 487, 2000, 2001, 2002, 2010, 2400, 2410, 2420, 2430, 6430, 6514, 6517 A, 7001) side-by-side in a standard 19-inch rack.

Model 4288-4 side-by-side rack mount kit — Mounts Model 6514 and a 5.25-inch instru-

ment (Models 195A, 196, 220, 224, 230, 263, 595, 614, 617, 705, 740, 775A, 6512) side-by-side in a standard 19-inch rack.

Carrying case

Model 1050 padded carrying case — A carrying case for Model 6514. Includes handles and

shoulder strap.

System electrometer features

Model 6514 is a 6½-digit high-performance system electrometer. It can measure voltage, current, resistance and charge. Details on its measurement capabilities are explained in Section 2 of this manual (see “Measurement Overview”).

Features of Model 6514 System Electrometer include:

• Setup storage — Five instrument setups (three user, GPIB defaults and factory defaults)

can be saved and recalled.

• mX+b and percent — These calculations provide mathematical manipulation of

readings.

• Relative — Null offsets or establish baseline values.

• Buffer — Store up to 2500 readings in the internal buffer.

• Limits — Set up to two stages of high and low reading limits to test devices.

• Digital I/O port — Four output lines and one input line to control external circuitry. Use

as an interface between limit tests and component handler.

• Analog outputs — Provides a 2V analog output for a full range input. Preamp out pro-

vides a driven guard for Volts, or can be used for external feedback measurements.

• External feedback — Extends the measurement capabilities of the electrometer; loga-

rithmic currents, non-decade current ranges and non-standard charge ranges.

• Remote interface — Model 6514 can be controlled using the IEEE-488 interface

(GPIB) or the RS-232 interface.

• GPIB programming language — When using the GPIB, the instrument can be pro-

grammed using the SCPI or DDC programming language.

Front and rear panel familiarization

Front panel summary

The front panel of Model 6514 is shown in Figure 1-1.

Figure 1-1

Model 6514 front panel

TALK LSTN

SRQ SHIFT TIMER

CH1REM

SCAN

STEP CH2 CH3 CH4 CH5 CH6 CH7 CH8 CH9 CH10

HOLD TRIG FAST MED SLOW AUTO ERR

REL FILT

BUFFER

Getting Started 1-5

MATH REAR

STAT

V-DROP

AUTO-DIS

CONF-LIM

GPIB

XFBK ZCHK

UNITS

CONF-ARM

SHIFT

LOCAL

POWER

MX+B

AVG

TEST CAL

STORE

MEDN

RCLL

Ω

VAL

REL LIMIT

SAVE SETUP

DELAY DAMP

6514 SYSTEM ELECTROMETER

RS-232

ZCOR

GRD

NPLC

RATEDIGIT

CONF-TRIG

EXIT ENTERHALT TRIG

RANGE

AUTO

RANGE

NOTE Most keys provide a dual function or operation. The nomenclature on a key indicates

its unshifted function/operation, which is selected by pressing the key. Nomenclature (in blue) above a key indicates its shifted function. A shifted function is selected by pressing the SHIFT key and then the function/operation key.

1 Special keys and power switch

SHIFT Use to select a shifted function or operation. LOCAL Cancels GPIB remote mode. POWER Power switch. In position turns 6514 on (I), out position turns it off (O).

2 Function and operation keys

Top Row

Unshifted V Selects voltage measurement function. I Selects current measurement function. Ω Selects resistance measurement function. Q Selects charge measurement function. XFBK Enables/disables External Feedback. ZCHK Enables/disables Zero Check. ZCOR Enables/disables Zero Correct. GRD Enables/disables Guard.

1-6 Getting Started

Shifted V-DROP Enables/disables V-drop measurements for Ω function. AUTO-DIS Sets and enables/disables Auto Discharge for charge measurements. GPIB Conﬁgures and enables/disables GPIB interface. RS-232 Conﬁgures and enables/disables RS-232 interface.

Middle Row

Unshifted AVG Conﬁgures and enables/disables digital ﬁlter. MEDN Conﬁgures and enables/disables median ﬁlter. REL Enables/disables Relative (Rel). LIMIT Performs conﬁgured limit tests. DIGIT Sets display resolution. RATE Selects measurement rate.

 and  Controls cursor position for making selections or editing values.

Shifted MX+B Conﬁgures and enables/disables mX+b math function. % Conﬁgures and enables/disables Percent math function. VAL Sets Rel value and enables Rel. CONF-LIM Conﬁgures limit tests. UNITS Selects engineering units for scientiﬁc notation for display readings. NPLC Set rate by setting PLC value.

Bottom Row

Unshifted STORE Sets the number of readings to store and enables the buffer. RCLL Displays stored readings (including maximum, minimum, peak-to-peak, average,

and standard deviation). The  and  range keys scroll through the buffer, and the 

or  key toggles between reading number and reading. DELAY Sets user delay between trigger and measurement. DAMP Enables/disables damping for current measurements. HALT Stops measurement process. Puts 6514 in idle state. TRIG Trigger measurement(s). Takes 6514 out of idle state. EXIT Cancels selection, moves back to measurement display. ENTER Accepts selection, moves to next choice or back to measurement display.

Shifted TEST Performs key-press test or display test. CAL Accesses calibration. SAVE Saves present setup to a memory location. SETUP Restores setup stored in a memory location, or to GPIB or factory defaults. CONF-ARM Conﬁgures Arm Layer of trigger model. CONF-TRIG Conﬁgures Trigger Layer of trigger model.

3 Range keys

 Selects the next higher voltage measurement range.  Selects the next lower voltage measurement range.

AUTO Enables/disables autorange.

4 Display annunciators

* (asterisk) Readings being stored in buffer. ↔ (more) Indicates additional selections are available. AUTO Autorange enabled. BUFFER Recalling readings stored in buffer. ERR Questionable reading, or invalid cal step. FAST Fast (0.1 PLC) reading rate selected. FILT Filter enabled. LSTN Instrument addressed to listen over GPIB. MATH mX+b or Percent (%) calculation enabled. MED Medium (1 PLC) reading rate selected. REL Relative enabled for present measurement function. REM Instrument in GPIB remote mode. SHIFT Accessing a shifted key. SLOW Slow reading rate selected; 6 PLC for 60Hz or 5 PLC for 50Hz. SRQ Service request over GPIB. STAT Displaying buffer statistics. TALK Instrument addressed to talk over GPIB bus. TIMER Timer controlled triggering in use. TRIG External triggering (GPIB or trigger link) selected.

5 Handle

Pull out and rotate to desired position.

Getting Started 1-7

1-8 Getting Started

Rear panel summary

The rear panel of Model 6514 is shown in Figure 1-2.

Figure 1-2

Model 6514 rear panel

INPUT 250V PK

INPUT PREAMP

OFF

V, GUARD

(PROGRAMMABLE)

PREAMP OUT

250V PK

GUARD

(FOLLOWS

INPUT)

(INTERNAL)

2V ANALOG

10K

OUTPUT

PREAMP

2V ANALOG

COM

COMMON CHASSIS

TRIGGER LINK

OUT

OUTPUT

LINE RATING

FUSE LINE

630mA

(SB)

315mAT

(SB)

50, 60Hz

60 VA MAX

100 VAC 120 VAC

220 VAC 240 VAC

RS232DIGITAL I/O

120

MADE IN

IEEE-488

(CHANGE IEEE ADDRESS

WITH FRONT PANEL MENU)

U.S.A.

789 10

1 INPUT

This standard 3-lug female triax connector is used to connect the signal to be measured to the input of Model 6514. Mates to a triax cable terminated with a 3-lug male triax connector.

2 PREAMP OUT

Provides a guard output for Volts measurements. Can be used as an inverting output or with external feedback for the Amps and Coulombs modes.

32V ANALOG OUTPUT

Provides a scaled DC output voltage. A full range input will result in a 2V analog output. For the volts function, the output is non-inverting.

4 COMMON

Use as input low, or the common for the 2V Analog Output and Preamp Out.

5 CHASSIS

This terminal is connected to the chassis of Model 6514 and to power line earth ground via the power line cord. For ﬂoating measurements (up to 500V peak), remove the ground link between COMMON and CHASSIS.

Getting Started 1-9

6 IEEE-488

Connector for IEEE-488 (GPIB) operation. Use a shielded cable, such as Models 7007-1 and 7007-2.

7 DIGITAL I/O

Male DB-9 connector for digital output lines and component handler signals.

8 TRIGGER LINK

Eight-pin micro-DIN connector for sending and receiving trigger pulses among connected instruments. Use a trigger link cable or adapter, such as Models 8501-1, 8501-2, 8502 and 8503.

9 RS-232

Female DB-9 connector for RS-232 operation. Use a straight-through (not null modem) DB-9 shielded cable.

10 Power module

Contains the AC line receptacle, power line fuse, and line voltage setting. The instrument can be conﬁgured for line voltages of 100V/120V/220V/240VAC at line frequencies of 50 or 60Hz.

1-10 Getting Started

Power-up

Line power connection

Perform the following procedure to connect Model 6514 to line power and turn on the

instrument.

1. Check to be sure the line voltage setting on the power module is correct for the operating

CAUTION Operating the instrument on an incorrect line voltage may cause damage to

2. Before plugging in the power cord, make sure the front panel power switch is in the off

3. Connect the female end of the supplied power cord to the AC receptacle on the rear

WARNING The power cord supplied with Model 6514 contains a separate ground wire

voltage in your area. The line voltage setting is indicated in the window on the power module (see Figure 1-2). The upside-down 120 setting is for line voltages of 100/ 120VAC, and the upside-down 240 setting is for line voltages of 220/240VAC. The procedure to change the line voltage setting is provided in Section 20.

the instrument, possibly voiding the warranty.

(O) position.

panel. Connect the other end of the power cord to a grounded AC outlet.

for use with grounded outlets. When proper connections are made, instrument chassis is connected to power line ground through the ground wire in the power cord. Failure to use a grounded outlet may result in personal injury or death due to electric shock.

4. Turn on the instrument by pressing the front panel power switch to the on (1) position.

Line frequency selection

During the power-up sequence, the selected line frequency setting is displayed. The line frequency setting can be changed from the front panel by holding in the TRIG key during the power-up sequence. This action toggles between 50 and 60Hz. The command to remotely set line frequency is listed in Table 1-1.

SCPI programming

Table 1-1

SCPI commands - line frequency

Command Description

SYSTem :LFRequency <freq> :LFRequency?

SYSTem Subsystem: Select power line frequency (in Hz); 50 or 60. Read present line frequency setting.

Power-up sequence

The following power-up sequence occurs when the Model 6514 is turned on:

1. The Model 6514 performs self-tests on its EPROM and RAM with all digits and annunciators turned on. If a failure is detected, the instrument momentarily displays an error message and the ERR annunciator turns on. Error messages are listed in Appendix B.

NOTE If a problem develops while the instrument is under warranty, return it to Keithley

Instruments Inc., for repair.

2. If the instrument passes the self-tests, the firm are revision levels are displayed. For example: 6514 REV: A01

3. The detected line frequency is then displayed. For example: FREQ: 60Hz

4. Lastly, information on the selected remote interface is displayed: a. GPIB — If the GPIB is the selected interface, the instrument will display the

selected language (SCPI or DDC) and primary address. Examples: SCPI ADDR: 14 DDC ADDR: 14 b. RS-232 — If RS-232 is the selected interface, the instrument will display the baud

rate setting. For example: RS-232: 9600b

Getting Started 1-11

1-12 Getting Started

Display

Readings can be displayed in engineering units or scientif c notation (see “Units” in Section 6 for details). Annunciators indicate various states of operation. See “Front Panel Summary” (presented earlier in this section) for a complete listing of display annunciators.

NOTE The Display and Keys Test allows you to test display digit segments and annunciators,

and check the functionality of front panel keys. These tests are accessed by pressing SHIFT and then TEST. Refer to Section 20 for details.

Status and error messages

Status and error messages are displayed momentarily. During operation and programming, you will encounter a number of front panel messages. Typical messages are either of status or error variety, as listed in Appendix B.

Default settings

Model 6514 can be restored to one of f ve default setup conf gurations; factory (FACT), GPIB and three user-saved (USR0, USR1 and USR2). As shipped from the factory, Model 6514 powers up to the factory default settings. Factory default settings provide a general purpose setup for front panel operation, while the GPIB default settings do the same for remote operation. Factory and GPIB default settings are listed in Table 1-2.

For front panel operation, the instrument will power up to whichever default setup was last saved or restored. For example, if you save the present instrument setup as USR0, the instrument will subsequently power up to the USR0 setup.

NOTE At the factory, the factory default setup is saved as the USR0, USR1 and USR2 setups.

Saving a user setup — Perform the following steps to save a user setup:

1. Configure Model 6514 for the desired measurement application.

2. Press SHIFT and then SAVE to access the save setup menu.

3. Use the 2 = USR2).

4. Press ENTER.

Restoring a setup — Perform the following steps to restore a setup:

1. Press SHIFT and then SETUP to display the restore menu:

2. Use the

3. Press ENTER.

▲ or ▼ key to display the desired memory location (0 = USR0, 1 = USR1,

▲ or ▼ key to display the desired setup (FACT, GPIB, USR0, USR1 or USR2).

Getting Started 1-13

Remote operation

Saving and restoring user setups — The *SAV and *RCL commands are used to save and

recall user setups. These commands are documented in Section 14.

Restoring factory or GPIB default setups — The SYSTem:PRESet command returns

Model 6514 to the factory defaults and the *RST command returns it to the GPIB defaults. The *RST command is documented in Section 14 and SYSTem:PRESet is covered in Section 16 (SYSTem Subsystem).

Selecting power-on setup — The SYSTem:POSetup command is used to select which setup

to return to on power-up. The SYSTem:POSetup command is documented in Section 16 (SYSTem Subsystem).

Table 1-2

Default settings

Setting Factory GPIB

Arm Layer (CONF-ARM):

Arm-In Source Event IMM IMM Arm Count INF 1 Input Trigger Link Line 1 1 Source Bypass NEVER NEVER Output Trigger Link Line 2 2 Output Trigger Off Off

Auto Discharge Off Off

Level 2e-6 2e-6

Buffer (STORE): Disabled Disabled

Count No effect No effect

Digital Filter (AVG): Off Off

Count 10 10

Type Moving Moving Display Resolution (DIGIT) 5½-digits 5½-digits Function Volts Volts Guard Off Off GPIB: No effect (On at factory) No effect (On at factory)

Address No effect (14 at factory) No effect (14 at factory)

Language No effect (SCPI at factory) No effect (SCPI at factory)

1-14 Getting Started

Table 1-2 (cont.)

Default settings

Setting Factory GPIB

Limit Tests:

Limit 1 and Limit 2: Disabled Disabled

Digital Output Pass Pattern 15 15 Auto-Clear Off Off

Line 4 Mode End of Test End of Test

Median Filter: Off Off

Rank 1 1

MX+B: Disabled Disabled

“M” Value 1.0 1.0 “B” Value 0.0 0.0 Units MXB MXB

Percent: Disabled Disabled

Reference 1.0 1.0 Range 20V Auto Rate: Slow Slow

NPLC 6.0 (60Hz) or 5.0 (50Hz) 6.0 (60Hz) or 5.0 (50Hz) Rel: Off Off

Rel Value (VAL) 0.0 0.0 RS-232: No effect (Off at factory) No effect (Off at factory)

All Settings No effect No effect Trigger Layer (CONF-TRIG):

Trig-In Source Event IMM IMM

Trigger Count 1 1

Trigger Delay 0 0

Input Trigger Link Line 1 1

Source Bypass NEVER NEVER

Output Trigger Link Line 2 2 Units No effect No effect V-Drop Disabled Disabled Zero Check Enabled Enabled Zero Correct Disabled Disabled

HI and LO Values 1, -1 1, -1 Digital Fail Output Patterns 15 15

Delay 0.00010 sec 0.00010 sec Output Clear Pattern 15 15

SCPI programming

SCPI programming information is integrated with front panel operation throughout this manual. SCPI commands are listed in tables, and additional information that pertains exclusively to remote operation is provided after each table. The SCPI tables may reference you to other sections of this manual.

NOTE Except for Section 17, most SCPI tables in this manual are abridged. That is, they

exclude most optional command words and query commands. Optional command words and query commands are summarized as follows.

Optional command words — In order to be in conformance with the IEEE-488.2 standard,

Model 6514 accepts optional command words. Any command word that is enclosed in brackets ([]) is optional and does not have to be included in the program message.

Query commands — Most command words have a query form. A query command is iden-

tified by the question mark (?) that follows the command word. A query command requests (queries) the programmed status of that command. When a query command is sent and Model 6514 is addressed to talk, the response message is sent to the computer.

NOTE For complete details, see “Programming Syntax” in Section 12.

Getting Started 1-15

Measurement Concepts

• Measurement overview — Explains the basic measurement capabilities of Model 6514.

• Performance considerations — Covers a couple of considerations that affect overall

performance; warm-up and autozero.

• Connection fundamentals — Covers fundamental information about connecting test

circuits to the electrometer.

• Zero check and zero correct — Provides operation information on these two important

aspects of the basic measurement process.

• Measurement considerations — Summarizes the various factors that affect low level

measurements.

2-2 Measurement Concepts

Measurement overview

The basic measurement capabilities of Model 6514 are summarized in Table 2-1. Accuracy

for each measurement function and range is listed in specif cations (Appendix A).

Table 2-1

Basic measurement capabilities

Function Reading Range Available Ranges

Volts ±10uV to ±210V 2V, 20V and 200V Amps ±100aA to ±21mA 20pA, 200pA, 2nA, 20nA, 200nA, 2uA, 20uA,

Ohms 10mΩ to 210GΩ 2kΩ, 20kΩ, 200kΩ, 2MΩ, 20MΩ, 200MΩ, 2GΩ,

Coulombs 10fC to 21µC 20nC, 200nC, 2µC, and 20µC

Performance considerations

200uA, 2mA and 20mA

20GΩ and 200GΩ

Warm-up period

Model 6514 can be used within one minute after it is turned on. However, the instrument should be turned on and allowed to warm up for at least one hour before use to achieve rated accuracy. If the instrument has been exposed to extreme temperatures, allow extra time for the internal temperature to stabilize.

Autozero

To help maintain stability and accuracy over time and changes in temperature, the Model 6514 periodically measures internal voltages corresponding to offsets (zero) and amplif er gains. These measurements are used in the algorithm to calculate the reading of the input signal. This process is known as autozeroing.

When autozero is disabled, the offset and gain measurements are not performed. This increases measurement speed. However, the zero and gain reference points will eventually drift resulting in inaccurate readings of the input signal. It is recommended that autozero only be disabled for short periods of time.

Autozero cannot be disabled from the front panel, however, it can be enabled from the front panel by restoring factory or GPIB default conditions.

SCPI programming

Table 2-2

SCPI commands — autozero

Command Description Default

SYSTem SYSTem Subsystem:

:AZERo

[:STATe] Enable or disable autozero. ON

Programming example

The following command sequence will perform one zero corrected amps measurement:

SYST:AZER OFF ‘ Disable autozero. SYST:AZER ON ‘ Enable autozero.

Connection fundamentals

Measurement Concepts 2-3

The following provides important fundamental information on input connections to Model

6514. Typical connection drawings are included with the various measurement procedures provided in subsequent sections of this manual.

Input connector

The rear panel INPUT connector is a 3-lug female triax connector that will mate to a cable

terminated with a male triax connector.

2-4 Measurement Concepts

Input conﬁgurations

As shown in Figure 2-1, the input connector can be conf gured in two ways. With guard off (Figure 2-1A), input low is connected to the inner shell of the connector. This configuration is used for Amps, Coulombs, unguarded Volts and unguarded Ohms measurements.

With guard on (Figure 2-1B), the driven guard is connected to the inner shell of the triax connector. Input low is accessed via the COMMON terminal through an internal 0.1Ω fuse. This configuration is used for guarded Volts and guarded Ohms measurements only. The GRD key toggles guard on and off.

NOTE The state of guard (on or off) has no affect on the Amps and Coulombs functions. The

unguarded configu ation is always selected for the Amps and Coulombs functions.

Figure 2-1

Input connector configurations

INPUT

250V PEAK

Volts, Amps, Ohms & Coulombs

A. Unguarded (GRD off)

Input High

Guard

Chassis

INPUT

250V PEAK

Volts and Ohms only

Ground

B. Guarded (GRD on)

Input High

Input Low

Chassis Ground

COMMON

<1Ω

Fuse

Input Low

Measurement Concepts 2-5

Maximum input levels

The maximum input levels to Model 6514 are summarized in Figure 2-2.

WARNING The maximum common-mode input voltage, which is the voltage between

the input (HI or LO) and chassis ground, is 500V peak. Exceeding this value may create a shock hazard.

CAUTION Connecting PREAMP OUT, COMMON, or 2V ANALOG OUTPUT to

earth while ﬂoating the input may damage the instrument.

Figure 2-2

Maximum input levels

Low noise input cables

ing low noise cables are recommended for use with Model 6514:

Input High

Max Input Signal *

Input Low

Chassis Ground

* Max Input Signal - 250V Peak, DC to 60Hz sine wave (10 seconds maximum in mA ranges).

500V Peak

When making precision measurements, you should always use low noise cables. The follow-

• Model 237-ALG-2 — This 2-meter low noise triax cable mates directly to the input connector of Model 6514. The other end is terminated with three alligator clips. The clip with the red boot is input high, black boot is input low or guard, and the green boot is chassis ground.

• Model 7078-TRX-3 — This 3-foot low noise triax cable is terminated with a 3-slot triax connector on either end.

• Models 7078-TRX-10 and 7078-TRX-20 — Same as Model 7078-TRX-3 except that they are 10 feet and 20 feet in length.

NOTE As a general rule, always use the shortest possible cable for volts, amps and ohms

measurements.

2-6 Measurement Concepts

Basic connections to DUT

Unguarded connections

Basic unguarded connections are shown in Figure 2-3, the DUT is the voltage, current, resistance or charge to be measured. Circuit high is connected to the center conductor of the input connector and circuit low is connected to the inner shell of the connector. For unguarded volts and ohms measurements, the driven guard (GRD) must be off.

Figure 2-3

Basic connections for unguarded measurements

INPUT

250V PK

NOTE:

DUT

For Volts and Ohms, GRD must be off.

Measurement Concepts 2-7

Noise and safety shields — Figure 2-4 shows typical shielding for unguarded measure-

ments. A noise shield is used to prevent unwanted signals from being induced on the electrometer input. Measurements that may benef t from effective shielding include unguarded volts and ohms, amps below 1uA, and low level coulombs.

Typically, the noise shield is connected to electrometer input LO. However, better noise performance may be achieved by connecting the noise shield to both input LO and chassis ground. Electrometer LO can be connected to chassis ground by installing the ground link between the COMMON and CHASSIS binding posts.

A safety shield is required whenever a hazardous voltage (>30V) is present on the noise shield or when the test circuit (DUT) is f oated above earth ground at a hazardous voltage level (see “Floating Measurements”). Connections for the safety shield is shown in Figure 2-4B. The metal safety shield must completely surround the noise shield or f oating test circuit, and it must be connected to safety earth ground using #18 AWG or larger wire.

Figure 2-4

Shielding for unguarded measurements

INPUT

250V PK

A. Noise Shield

Chassis Ground

INPUT

250V PK

B. Safety Shield

DUT

Metal Noise Shield

Metal Safety Shield

Safety Earth Ground

2-8 Measurement Concepts

Guarded connections

The basic guarded connections for volts and ohms are shown in Figure 2-5. For these measurements, circuit high is connected to the center conductor of the input connector while circuit low is connected to the COMMON banana jack terminal. With guard (GRD) on, the driven guard is available at the inner shell of the triax connector which is connected to the metal guard plate.

WARNING The guard voltage is at the same potential as the input. Therefore, hazard-

WARNING With an open input, up to 250V peak may be present on the guard terminals

The driven guard is used to eliminate leakage current and capacitance in high impedance circuits which could corrupt the volts or ohms measurement. The concept of guarding techniques are covered in Section 3.

ous voltage on the input will also be present on the guard plate. To prevent electric shock, always use a metal safety shield (as shown in Figure 2-5) for guarded voltage measurements above 30Vrms (42V peak). The metal safety shield must be connected to safety earth ground using #18 AWG or larger wire.

while in Volts or Ohms. To prevent this, enable zero check whenever the input is open.

Figure 2-5

Basic connections for guarded measurements

Measure Volts

INPUT

250V PK

COMMON

Measure Ohms

INPUT

250V PK

COMMON

Chassis Ground

GRD

Chassis Ground

GRD

NOTE: GRD must be on.

Metal Guard Plate

Safety Earth Ground

Metal Guard Plate

Ω

Safety Earth Ground

Metal Safety Shield

Test ﬁxture

Whenever possible, use a shielded low leakage test f xture to make precision measurements. A general purpose test f xture is shown in Figure 2-6. This test fixture will accommodate a variety of connection requirements.

Measurement Concepts 2-9

Figure 2-6

General purpose test fixture

Metal Chassis

To External

Source

To 6514

Input

To 6514

COMMON

Banana Jacks

3-Lug Female Triax Connector

Metal Guard Plate

DUT

Insulated Terminal Post (6)

Test ﬁxture chassis

• The chassis of the test f xture should be metal so that it can function as a shield for the DUT or test circuit. The metal chassis should be connected to chassis ground of Model 6514 via the triax cable.

• The test box must have a lid that closes to prevent contact with live circuitry.

• The test fixture must have a screw terminal that is used exclusively for connection to safety earth ground.

Safety Earth Ground

WARNING To provide protection from shock hazards, the test ﬁxture chassis must be

properly connected to safety earth ground. A grounding wire (#18 AWG or larger) must be attached securely to the test ﬁxture at a screw terminal designed for safety grounding. The other end of the ground wire must be attached to a known safety earth ground.

Guard plate

A metal guard plate will provide guarding or noise shielding for the DUT or test circuit. It will also serve as a mounting panel for DUT or test circuits. The guard plate must be insulated with 1000V spacing from the chassis of the test f xture.

2-10 Measurement Concepts

Connectors, terminals and internal wiring

Basic connector requirements include a 3-lug female triax connector, and three banana jacks. One banana jack is used to make the COMMON connection to the electrometer for guarded measurements. The other two banana jacks will accommodate connection to an external power supply. The banana jacks must be insulated from the chassis of the test f xture. The outer shell of the triax connector must be referenced to chassis ground. Therefore, DO NOT insulate the outer shell of the triax connector from the metal chassis of the test f xture.

DUT and test circuits are to be mounted on the guard plate using insulated terminals. To minimize leakage, select terminals that use virgin Teflon insulators.

Inside the test f xture, use an insulated wire to connect the inner shell of the triax connector to the guard plate. For unguarded measurements, the guard plate will serve as a noise shield. For the volts and ohms functions, turning GRD on will connect guard to the guard plate.

Handling and cleaning test ﬁxtures

Dust, body oil, solder f ux, and other contaminants on connector and terminal insulators can significantly decrease the leakage resistance resulting in xcessive leakage currents. Contaminants on DUT and test circuit components can create a leakage path. The leakage currents may be large enough to corrupt low-level measurements.

Handling tips:

• Do not touch the bodies of DUT or test circuit components. If you cannot handle them by their leads, use clean cotton gloves to install them in the test f xture.

• Do not touch any connector or terminal insulator.

• If installing a test circuit that is on a PC board, handle the board by the edges. Do not touch any board traces or components.

Cleaning tips:

• Use dry nitrogen gas to clean dust off connector and terminal insulators, DUT, and other test circuit components.

• If you have just built the test f xture, remove any solder flux using methanol along with clean foam-tipped swabs or a clean soft brush. Clean the areas as explained in the next tip.

•To clean contaminated areas, use methanol and clean foam-tipped swabs. After cleaning a large area, you may want to flush the area with methanol. Blow dry with dry nitrogen gas.

• After cleaning, the test f xture (and any other cleaned devices or test circuits) should be allowed to dry in a 50

C low-humidity environment for several hours.

Input protection

a high voltage (>250V) and resultant current surge could damage the input circuitry. A typical test circuit to measure the leakage current of a capacitor is shown in Figure 2-7. When Switch S is closed, an initial charging current will f ow and the high voltage will be seen across the input of Model 6514.

Figure 2-7

Capacitor test circuit without protection

extra protection. The resistor must be large enough to limit the current through the diodes to 10mA or less, and be large enough to withstand the supply voltage. The protection circuit should be enclosed in a light-tight conductive shield.

Measurement Concepts 2-11

Model 6514 incorporates protection circuitry against nominal overload conditions. However,

Capacitor

Under Test

6514

Ammeter

Adding a resistor and two diodes (1N3595) as shown in Figure 2-8 will provide considerable

Figure 2-8

Capacitor test circuit with protection

Floating measurements

Protection Circuit

Capacitor

Under Test

D1 D2

6514

Ammeter

With the ground link between the COMMON and CHASSIS banana jack terminals removed, Model 6514 can perform f oating measurements up to 500V above chassis ground. These measurements can result in safety concerns.

2-12 Measurement Concepts

Figure 2-9 shows two examples where Model 6514 f oats at a hazardous voltage level. In Figure 2-9A, a shock hazard (100V) exists between meter input LO and chassis ground. If meter input LO is connected to a noise shield, then the shock hazard will also be present on that shield.

In Figure 2-9B, a shock hazard (200V) exists between the meter input (HI and LO) and chassis ground. If meter LO is connected to a shield, then the shock hazard will also be present on that shield.

Figure 2-9

Floating measurements

200V

= R2)

A. Voltage measurement

200V

B. Current measurement

6514

Voltmeter

6514

Ammeter

100V

200V

WARNING The maximum voltage (common-mode) between electrometer LO and chas-

sis ground is 500V. Exceeding this value may create a shock hazard.

WARNING When ﬂoating input LO above 30V from earth (chassis) ground, hazardous

voltage will be present at the analog outputs (PREAMP OUT and 2V ANALOG OUTPUT). Hazardous voltage may also be present when the input voltage exceeds 30V in the Volts function.

CAUTION Connecting PREAMP OUT, COMMON or 2V ANALOG OUTPUT to

earth (chassis) ground while ﬂoating the input may damage the instrument.

Zero check and zero correct

Table 2-3 lists the display messages associated with zero check and zero correct. The

two-character message is displayed along with the reading.

Table 2-3

Display messages for zero check and zero correct

Display Message

ZC On Off ZZ On On CZ Off On

Zero check

When zero check is enabled (on), the input amplif er is reconf gured to shunt the input signal to low as shown in Figure 2-10. With zero check enabled, it will remain enabled when a different function is selected. With zero check disabled, it will remain disabled when the volts, amps or coulombs function is selected.

Zero Check Zero Correct

Measurement Concepts 2-13

NOTE Zero check will always enable whenever the ohms function is selected.

Zero check is enabled by pressing the ZCHK key. Pressing ZCHK a second time disables zero check.

NOTE To ensure proper operation, always enable zero check before changing functions.

For coulombs, enabling zero check dissipates the charge. That is, the charge reading is reset to zero. When zero check is disabled, a sudden change in the charge reading (zero check hop) occurs. This effect can be cancelled by enabling Relative (REL) immediately after zero check is disabled. Relative is explained in Section 7.

2-14 Measurement Concepts

For volts, amps and ohms, leave zero check enabled when connecting or disconnecting input

signals. For coulombs, disable zero check before connecting the input signal. If zero check is left enabled when you connect the input signal, the charge will dissipate through the 10MΩ resistor (see Figure 2-10).

Figure 2-10

Equivalent input impedance with zero check enabled

Input

10MΩ

Input

10MΩ

Zero correct

Model 6514 has a zero correct feature to algebraically subtract the voltage offset term from

the measurement. Perform the following steps to zero correct the volts or amps function:

NOTE The ZCOR key toggles zero correct on and off. If zero correct is enabled (“ZZ” or

CIN = 10pF

= 1kΩ (mA)

1MΩ || 1000pF (µA) 1GΩ || 10pF (nA) 1TΩ || 1pF (pA)

Input

CIN = 10pF

10MΩ

Amps

Volts and Ohms

CIN = 10pF

Input

CIN = 10pF

“CZ” message displayed), press ZCOR to disable it.

1kΩ (kΩ)

1MΩ || 1000pF (MΩ) 1GΩ || 10pF (GΩ)

10MΩ

Coulombs

= 1000pF (20nC, 200nC)

0.1µF (2µC, 20µC)

Ohms

1. Select the volts (V) or amps (I) function.

2. Enable zero check (“ZC” message displayed).

3. Select the range that will be used for the measurement, or select the lowest range.

4. Press ZCOR to enable zero correct (“ZZ” message displayed).

5. Press ZCHK to disable zero check.

6. Readings can now be taken from the display. The “CZ” message indicates that the displayed reading is zero corrected.

Measurement Concepts 2-15

NOTES Zero check will enable whenever the ohms function is selected.

Model 6514 will remain zeroed even if it is upranged. If downranged, re-zero the instrument.

Model 6514 does not have to be re-zeroed as long as the ambient temperature remains stable.

Zero correction cancels the voltage offset term of the amplif er. With both zero check and zero correct enabled, the instrument may not display a perfectly zeroed reading.

If Model 6514 is operating at, or near T T

is the internal temperature of Model 6514 when it was last calibrated.

CAL

, zero correction will have very little affect.

CAL

SCPI programming — zero check and zero correct

Table 2-4

SCPI commands — zero check and zero correct

Commands Description Default Ref

SYSTem SYSTem Subsystem:

:ZCHeck Enable or disable zero check. ON :ZCORrect Zero correct:

[:STATe] Enable or disable zero correct. OFF A :ACQuire Acquire a new zero correct value. B

INITiate Trigger a reading. B

A) SYST em:ZCORrect[:ST A Te]

This method to perform zero correction is consistent with the way it is performed from the

front panel. That is, zero correction is performed while zero check is enabled:

SYST:ZCH ON ‘ Enable zero check. SYST:ZCOR ON ‘ Perform zero correction.

A second method to perform zero correction is to f rst acquire the zero correct value (see

Ref. B).

2-16 Measurement Concepts

B) SYST em:ZCORrect:ACQuire

The zero correct value can only be acquired while zero check is enabled. The internal offset will become the correction value. Zero correction can then be performed with zero check disabled. This acquire method makes it convenient if you need to re-zero the selected function often.

The following command sequence uses the acquire method to zero correct the 2V range:

SYST:ZCH ON ‘ Enable zero check.

FUNC ‘VOLT’ ‘ Select Volts function.

VOLT:RANG 2 ‘ Select 2V range.

INIT ‘ Trigger one reading.

SYST:ZCOR:ACQ ‘ Acquire zero correct value.

SYST:ZCH OFF ‘ Disable zero check.

SYST:ZCOR ON ‘ Perform zero correction.

The INITiate command in the above sequence is used to trigger a reading. This reading is the offset that is acquired as the zero correct value. See Section 9 for more information on INITiate.

NOTE Sending the :ACQuire command while zero check is disabled will result in an error.

The command will not be executed.

Measurement Concepts 2-17

Input bias current and offset voltage calibration

The input bias current and offset voltage calibration procedures that follow should be performed periodically to actively cancel input bias current and offset voltage, optimizing measurement accuracy, particularly at low levels.

Front panel

Front panel input bias current calibration

1. Access the front panel calibration menu by pressing SHIFT then CAL.

NOTE See Section 19 for details on other calibration menu selections.

2. From the calibration menu, use the down RANGE key to display the following: CAL: IOFFSET

3. Press ENTER. The instrument will prompt for the triax shielding cap as follows: INPUT CAP

4. Connect a triax shielding cap to the rear panel INPUT jack. (Use a Keithley CAP-31 or equivalent.)

5. Press ENTER to complete input bias current calibration.

6. If you wish to perform front panel offset voltage calibration, proceed to Step 2 of the procedure below. Otherwise, press EXIT to return to normal display.

Front panel offset voltage calibration

1. Access the front panel calibration menu by pressing SHIFT then CAL.

2. From the calibration menu, use the up or down RANGE key to display the following: CAL: VOFFSET

3. Press ENTER. The instrument will prompt for a short: INPUT SHORT

4. Connect a triax short to the rear panel INPUT jack. (Use the supplied Model 237-ALG2 triax cable or equivalent with red and black alligator clips connected together.)

5. Press ENTER to complete offset voltage calibration.

6. Press EXIT to return to normal display.

2-18 Measurement Concepts

SCPI programming

Table 2-5 lists SCPI commands used for input bias current and offset voltage calibration.

Table 2-5

SCPI commands — input bias current and offset voltage calibration

Commands Description

:CALibration:UNPRotected:IOFFset :CALibration:UNPRotected:VOFFset

Input bias current calibration. Offset voltage calibration.

SCPI command input bias current calibration

1. Connect a triax shielding cap to the rear panel INPUT jack. (Use a Keithley CAP-31 or equivalent.)

2. Send the following command to perform input bias current calibration: :CAL:UNPR:IOFF

3. Allow the Model 6514 to complete the calibration process.

SCPI command offset voltage calibration

1. Connect a triax short to the rear panel INPUT jack. (Use the supplied Model 237-ALG-2 triax cable or equivalent with red and black alligator clips connected together.)

2. Send the following command to perform offset voltage calibration: :CAL:UNPR:VOFF

3. Allow the Model 6514 to complete the calibration process.

Measurement Concepts 2-19

Measurement considerations

There are a variety of factors to consider when making low level measurements. These considerations are listed and summarized in Table 2-6. For comprehensive information on all measurement considerations, refer to the Low Level Measurements handbook, which is available from Keithley Instruments.

Table 2-6

Summary of measurement considerations

Considerations Description

For V and Ω measurements: See Section 3 for details

Loading effects Circuit loading caused by a high impedance voltage source. Cable leakage resistance For unguarded measurements, leakage resistance in the triax cable

(between HI and LO) shunts the voltage to be measured.

Input capacitance (settling time)

Guarding input cable Eliminates the effects of leakage resistance for high impedance

At very high resistance levels, effects of cable capacitance can slow

down measurement response time.

measurements and input capacitance when using a long input cable.

For I measurements: See Section 4 for details

Input bias current Offset current of Model 6514 could affect low current

measurements.

Voltage burden Offset voltage of Model 6514 could cause errors if it is high in

relation to the voltage of the measured circuit.

Noise Noise generated by source resistance and source capacitance.

For Q measurements: See Section 5 for details

Input bias current Offset current of Model 6514 is integrated along with the input

signal, affecting the f nal reading. External voltage source Input current to Model 6514 should be limited to <1mA. Zero check hop Sudden change in the charge reading when zero check is turned off. Auto-discharge hop Sudden change in the charge reading when auto-discharge resets the

charge reading to zero.

2-20 Measurement Concepts

Table 2-6 (cont.)

Summary of measurement considerations

Considerations Description

For all measurements: See Appendix C for details

Ground loops Multiple ground points can create error signals. Triboelectric effects Charge currents generated in a cable by friction between a conductor

and the surrounding insulator (i.e. bending a triax cable).

Piezoelectric and stored charge effects

Currents generated by mechanical stress on certain insulating materials.

Electrochemical effects Currents generated by the formation of chemical batteries on a

circuit board caused by ionic contamination.

Humidity Reduces insulation resistance on PC boards and test connection

insulators.

Light Light sensitive components must be tested in a light-free

environment. Electrostatic interference Charge induced by bringing a charged object near your test circuit. Magnetic field The presence of magnetic f elds can generate EMF (voltage). Electromagnetic interference

(EMI)

EMI from external sources (i.e. radio and TV transmitters) can

affect sensitive measurements.

Volts and Ohms

Measurements

• Measurement overview — Summarizes the volts and ohms measurement capabilities of

Model 6514.

• Guarding — Explains guarding and the benef ts derived from it for high-impedance

volts and ohms measurements.

• Volts and ohms measurement procedure — Provides the procedure to measure volts

and ohms.

• SCPI programming — Covers the basic SCPI command used for the volts and ohms

functions.

• Volts and ohms measurement considerations — Covers measurement considerations

that apply to volts and ohms measurements.

• Application — Shows how to measure dielectric absorption of a capacitor.

3-2 Volts and Ohms Measurements

Measurement overview

Volts measurements — Model 6514 can make volts measurements from 10µV to 210V

using three measurement ranges; 2V, 20V, and 200V.

Ohms measurements — Model 6514 makes ohms measurements by sourcing a test current

and measuring the voltage drop across the DUT. The resistance reading is then calculated (R = V/1) and displayed. The electrometer can make ohms measurements from 10mΩ to 210GΩ using nine measurement ranges; 2kΩ, 20kΩ, 200kΩ, 2MΩ, 20MΩ, 200MΩ, 2GΩ, 20GΩ,and 200GΩ.

NOTE Accuracy specifications for all measurement functions are provided in Appendix A.

Guarding

The purpose of guarding is to eliminate the effects of leakage resistance and capacitance, that can exist between input HI and input LO. This leakage resistance and capacitance could adversely affect high-impedance measurements.

Test circuit leakage

In a test circuit, leakage current can occur through the insulators of the terminals for the DUT (device under test). In Figure 3-1, the test circuit consists of a current source in series with the DUT. The objective is to make an accurate voltage measurement of the DUT.

In Figure 3-1A, a resistance leakage path through the insulators (RL1 and RL2) shunts current around the DUT. If this leakage current is high in comparison to the DUT current, signif cant measurement error will occur. To keep error <0.1%, the leakage resistance must be 1000 times greater than the resistance of the DUT. For example, if the nominal resistance of the DUT is 100MΩ, leakage resistance must be >100GΩ.

Figure 3-1B shows how to use guarding to eliminate the effects of leakage resistance. With GRD enabled, the driven guard, which is at the same potential as input HI, is connected to the metal mounting plate (now known as the guard plate). With both ends of RL1 at the same potential, current will not f ow through the insulator. With no current leakage path, all current f ows through the DUT allowing an accurate voltage measurement.

The above explanation also pertains to ohms measurements. The only difference is that the test current is provided by Model 6514.

Volts and Ohms Measurements 3-3

Figure 3-1

High-impedance voltage measurements

6514

COMMON

GRD Disabled

A. Unguarded

6514

GRD

COMMON

GRD Enabled

Insulator

(one of two)

RL1

Insulator

(one of two)

RL1

DUT

RL2

Leakage Path

Metal Mounting Plate

DUT

Metal Mounting Plate

B. Guarded

Input cable leakage and capacitance

In a similar manner to leakage in the test circuit, leakage in the input cable could also corrupt high-impedance measurements. In the unguarded mode, leakage in a triax cable occurs between the center conductor (HI) and the inner shield (LO).

Inherently, an input cable has capacitance that is formed by the center conductor (HI), inner shield (LO) and the insulator between them. For high-impedance measurements, the RC time constant can signif cantly slow down measurement response.

To minimize the effects of cable leakage, and input capacitance, keep the input cable as short as possible and use guard. With guard enabled, the same potential is applied to both the center conductor and inner shield of the cable. This eliminates leakage current and capacitor charging/ discharging.

NOTE Detailed information on "Cable Leakage Resistance”, “Input Capacitance (Settling

Time)” and “Guarding Input Cables” is provided in “Volts and Ohms Measurement Considerations” (located in this section).

3-4 Volts and Ohms Measurements

Volts and ohms measurement procedure

CAUTION The maximum input voltage to Model 6514 is 250V peak. Exceeding this

value may cause damage to the instrument that is not covered by the warranty.

WARNING The maximum common-mode input voltage, which is the voltage between

the input (HI or LO) and chassis ground, is 500V peak. Exceeding this value may create a shock hazard.

Step 1 Enable zero check and select the volts (V) or ohms (Ω) function

Zero check should always be enabled before making function or connection changes. The ZCHK key toggles zero check on and off. When on, the “ZC” or “ZZ” message is displayed. See Section 2 for details on zero check.

The volts function is selected by pressing the V key, and the ohms function is selected by pressing the Ω key.

NOTE Zero check will enable whenever the ohms function is selected.

Step 2 Enable or disable guard

The GRD key toggles the driven guard on and off. If performing unguarded measurements, press GRD until the “GUARD OFF” message is displayed. If performing guarded measurements, press GRD until the “GUARD ON” message is displayed.

WARNING Hazardous voltage may be present on the inner shield of the triax cable

when GRD is on. A metal safety shield connected to safety earth ground (as shown in Figure 3-5) must be used for voltage measurements at or above 30V.

Step 3 Perform zero correction (volts only)

To achieve optimum accuracy for low voltage measurements, it is recommended that you zero correct the electrometer. To do so, select the 2V range (which is the lowest range) and press the ZCOR key until the “ZZ” message is displayed. See Section 2 for details on zero correction.

Step 4 Select a manual measurement range or enable auto range

Use the RANGE  and  keys to select a manual measurement range, or press AUTO to enable auto range. With auto range enabled, the instrument will automatically go to the most sensitive range to make the measurement. See Section 6 for details on range.

Volts and Ohms Measurements 3-5

Step 5 Connect the DUT to the electrometer

NOTE Fundamental information on making connections to the electrometer input is pro-

vided in Section 2 (“Connection Fundamentals”).

WARNING A metal safety shield is required whenever a hazardous voltage (>30V) is

present on a noise shield or guard shield. As shown in Figures 3-2 and 3-3, the safety shield must be connected to safety earth ground using #18 AWG wire or larger.

Unguarded connections — Connections for unguarded volts and ohms measurements are

shown in Figure 3-2, where the DUT is the voltage or resistance to be measured. If a hazardous voltage (>30V) is present on the noise shield, or the test circuit is f oating above earth ground at a hazardous voltage level, a safety shield must be used as shown.

Figure 3-2

Connections for unguarded volts and ohms

237-ALG-2

Cable

Red (HI)

(Chassis)

Black (LO)

PREAMP OUT

INPUT 250V PK

INPUT PREAMP

OFF

GUARD

(FOLLOWS

V, GUARD

INPUT)

(PROGRAMMABLE)

GRD Disabled

Green

250V PK

(INTERNAL)

2V ANALOG

10K

OUTPUT

PREAMP

2V ANALOG

COM

DUT

COMMON CHASSIS

TRIGGER LINK

OUT

OUTPUT

6514 Rear Panel

LINE RATING

50, 60Hz

60 VA MAX

FUSE LINE

630mA

100 VAC

(SB)

120 VAC

220 VAC

315mAT

240 VAC

(SB)

Metal Noise Shield

Metal Safety Shield

Safety Earth Ground

RS232DIGITAL I/O

120

MADE IN

IEEE-488

(CHANGE IEEE ADDRESS

WITH FRONT PANEL MENU)

U.S.A.

3-6 Volts and Ohms Measurements

Guarded connections — Connections for guarded volts and ohms measurements are shown

in Figure 3-3. The driven guard (GRD) must be enabled for these measurements.

WARNING With an open input, up to 250V peak may be present on the guard terminals

while in Volts or Ohms. To prevent this, make sure zero check is enabled whenever the input is open.

Figure 3-3

Connections for guarded volts and ohms

237-ALG-2

Metal Guard Plate

Cable

INPUT 250V PK

INPUT PREAMP

OFF

V, GUARD

(PROGRAMMABLE)

Red (HI)

(GRD)

GUARD

(FOLLOWS

INPUT)

Black

Green

(Chassis)

PREAMP OUT

250V PK

(INTERNAL)

2V ANALOG

OUTPUT

10K

DUT

PREAMP

2V ANALOG

COM

COMMON CHASSIS

TRIGGER LINK

OUT

OUTPUT

6514 Rear Panel

Metal Safety Shield

Safety Earth Ground

LINE RATING

50, 60Hz

60 VA MAX

FUSE LINE

630mA

100 VAC

(SB)

120 VAC

220 VAC

315mAT

240 VAC

(SB)

MADE IN

U.S.A.

IEEE-488

(CHANGE IEEE ADDRESS

WITH FRONT PANEL MENU)

RS232DIGITAL I/O

120

GRD Enabled

Step 6 Disable zero check and take a reading from the display

V-Drop and I-Source for ohms

Model 6514 performs ohms measurement by sourcing a known test current through the DUT and then measuring the voltage drop across it. The resistance reading is then calculated (R = V/I) and displayed.

While the electrometer is measuring ohms, the test current through the DUT and the voltage

drop across it can be displayed as follows:

V-Drop — While displaying an ohms reading, press SHIFT and then Ω to display the voltage

drop across the DUT. The “VΩ” message will indicate that a V-Drop reading is being displayed. To return to the normal ohms reading, again press SHIFT and then Ω.

Test current — While displaying an ohms or V-Drop reading, press the Ω key. The test cur-

rent (ISRC) will be displayed for as long as you hold the key down.

WARNING The ohms function has a 250V compliance. To prevent electric shock,

always enable zero check to disable the test signal before making or breaking connections to DUT.

SCPI programming

Table 3-1

SCPI commands — volts and ohms function

Commands Description Default Ref

[SENSe] SENSe Subystem:

:FUNCtion <name> Select function; ‘VOLTage’ or ‘RESistance’. VOLT A :DATA? Return latest “raw” reading. B :VOLTage

:GUARd Enable or disable guard. OFF C

:RESistance

:GUARd Enable or disable guard. OFF C

Volts and Ohms Measurements 3-7

INITiate Trigger one or more readings. B READ? Trigger and return reading(s). B

A) SENSe:FUNCtion <name>

Parameters ‘VOLTage’ Volts function

‘RESistance’ Ohms function ‘CURRent’ Amps function ‘CHARge’ Coulombs function

Note that the parameter names are enclosed in single quotes (‘). However, double quotes (“)

can instead be used. Each measurement function “remembers” its own unique range setting.

3-8 Volts and Ohms Measurements

B) SENSe:DATA?

This command does not trigger a reading. It simply returns the last “raw” reading string. It will not return the result of any instrument calculation. The reading ref ects what is applied to the input.

To return a fresh (new) reading, you can send the INITiate command to trigger one or more readings before sending :DATA?. Details on INITiate are provided in Section 9.

While Model 6514 is busy performing measurements, the :DATA? command will not return the reading string until the instrument f nishes and goes into the idle state.

NOTES The format that the reading string is returned in is set by commands in the FORMat

Subsystem (see Section 16).

If there is no reading available when :DATA? is sent, an error (-230) will occur.

The READ? command can be used to return “fresh” readings. This command triggers and returns the readings. See Section 15 for details.

C) :GUARd Commands

Either of the two guard commands (VOLTage:GUARd or RESistance:GUARd) can be used to control the state of guard.

Programming example

The following command sequence will perform one zero corrected voltage measurement on the 2V range:

*RST ‘ Return to RST defaults. SYST:ZCH ON ‘ Enable zero check. VOLT:GUAR ON ‘ Enable guard. FUNC ‘VOLT’ ‘ Select Volts function. VOLT:RANG 2 ‘ Select 2V range. SYST:ZCOR ON ‘ Perform zero correction. SYST:ZCH OFF ‘ Disable zero check. READ? ‘ Trigger and return one reading.

Volts and Ohms Measurements 3-9

Volts and ohms measurement considerations

NOTE Since Model 6514 uses the source I measure V (calculate R) technique to measure

resistance, measurement considerations that apply to the volts function also apply to the ohms function.

Some considerations for making accurate volts and ohms measurements are summarized as follows. Additional measurement considerations are covered in Appendix C. For comprehensive information on precision measurements, refer to the Low Level Measurements handbook, which is available from Keithley Instruments.

Loading effects

Circuit loading can be detrimental to high-impedance voltage measurements. To see how meter loading can affect accuracy, refer to Figure 3-4. R of the source, while R

represents the input resistance of the meter. The percent error due to

loading can be calculated using the formula in the illustration. To keep the error under 0.1%, the input resistance (R

) must be about 1000 times the value of the source resistance (RS). The input

resistance of Model 6514 is >200TΩ. Therefore, to keep the error under 0.1%, the source resistance of the measured voltage must be <200GΩ.

represents the resistance component

Figure 3-4

Meter loading

Cable leakage resistance

Source

100R

% Error =

RS + R

Meter

In an unguarded voltage measurement, leakage current occurs in the input triax cable between the center conductor (HI) and the inner shield (LO). This leakage resistance shunts the voltage source to be measured. If the resistance of the source is not signif cantly less than the leakage resistance of the cable, measurement errors will occur.

The effects of leakage resistance can be eliminated by using guard to make high impedance voltage measurements. See “Guarding Input Cable” for more information. In general, guarding should be used when DUT resistance is 10

Ω or greater.

3-10 Volts and Ohms Measurements

Input capacitance (settling time)

The settling time of the circuit is particularly important when making volts measurements of a source that has high internal resistance (Figure 3-5A), or when making high-resistance ohms measurements (Figure 3-5B).

In both cases, the shunt capacitance (C) has to fully charge before an accurate voltage measurement can be made by V mined by the RC time constant (one time constant, of Figure 3-6 results. Therefore, it becomes necessary to wait four or f ve time constants to achieve an accurate reading. For example, if R = 100G( and the input cable has a nominal capacitance of 10pF, the RC time constant would be 1 second. If 1% accuracy is required, a single measurement would require at least f ve seconds.

There are two basic ways to minimize this problem: (1) keep capacitance in the system to an absolute minimum by keeping connecting cables as short as possible, and (2) use guarding. There is, however, a limit to how short the cable can be. Using guard can reduce these effects by up to a factor of 1000 (see “Guarding Input Cable”).

of Model 6514. The time period for charging the capacitor is deter-

τ = RC), and the familiar exponential curve

Volts and Ohms Measurements 3-11

Figure 3-5

Effects of input capacitance

Measured Source

6514

Voltmeter

τ = RC

A. High-Impedance Volts Measurement (Unguarded)

Measured Resistance

6514

Ohmmeter

τ = RC

B. High-Impedance Ohms Measurement (Unguarded)

3-12 Volts and Ohms Measurements

Figure 3-6

Settling time

Guarding input cable

ments that use long input cables.

3-7. E represents the leakage resistance and cable capacitance of the triax input cable. The equivalent circuit shows the divider that is formed. If R uate the voltage seen at the input of Model 6514 (see “Cable Leakage Resistance”). Also, R the cable capacitance (C response (see “Input Capacitance”).

Figure 3-7

Unguarded input cable

100

Percent of Final Value

Time

0 1.0 2.0 3.0 4.0 5.0

Guarding should be used for high-impedance measurements and for low voltage measure-

To better understand the concept of guarding, review the unguarded circuit shown in Figure

and R

represents the resistance and voltage components of the source, and RL and CL

is large enough, the divider will signif cantly atten-

) could create a long RC time constant resulting in a slow measurement

Center

Source

Triax Cable

Conductor

and

Equivalent Circuit

To 6514

Input

Inner Shield

To 6514

Input

Volts and Ohms Measurements 3-13

Guarding the circuit minimizes these effects by driving the inner shield of the triax cable at signal potential, as shown in Figure 3-8. Here, a unity gain amplifier with a high input impedance and low output impedance is used. Since the center conductor (HI) and the inner shield (Guard) of the cable are at virtually the same potential, the potential across R rent fl ws. Also, with a zero potential across C

, there is no capacitor charging process to slow

is zero, so no cur-

down the measurement response.

For the volts and ohms functions, the input of Model 6514 places the driven guard on the inner shield of the triax cable when GRD is enabled.

Figure 3-8

Guarded input cable

Source

Center

Triax Cable

Inner Shield

Conductor

A = I

6514 Input

150kΩ

Guard

3-14 Volts and Ohms Measurements

Application

Capacitor dielectric absorption

Dielectric absorption occurs when randomly oriented permanent dipoles of molecules with a capacitor dielectric are aligned by an applied electric f eld. After a capacitor has been disconnected from a discharge circuit, a residual charge remains on the capacitor, and a voltage will be re-established across the capacitor terminals.

For timing and integrating applications, dielectric absorption (or a residual capacitor voltage) can seriously degrade the accuracy of the circuit. Thus, a capacitor’s dielectric absorption must be known and compensated for in circuits where capacitance tolerance is a signif cant factor in circuit accuracy.

Dielectric absorption is not normally specif ed by a manufacturer since its importance is application dependent. The parameter can be def ned as the capacitor’s discharge current at a designated time following the initiation of a discharge cycle. The capacitor is typically charged up to the maximum voltage that will be applied. The measurement of the discharge current is usually made at a discharge time interval that will be used in the application of the device, or no longer than one minute. Acceptable capacitors have current levels below a required maximum limit.

Dielectric absorption can also be expressed as a percentage of residual voltage with respect to a charging voltage. This ratio is determined by charging the capacitor to the rated voltage. The capacitor is then discharged for a second time interval. Finally, the capacitor is open-circuited, and the residual voltage across the capacitor is measured after a third time constant.

The Model 6514 is particularly useful in measuring dielectric absorption because it draws virtually no charge from the capacitor during the measurement, nor does it induce charge on the capacitor being measured.

The test circuit in Figure 3-9A uses Keithley Model 230 as a voltage source and Model 6514 to perform the voltage measurements. Figure 3-9B shows the voltage waveform across the capacitor during the three phases of the test.

Initially, capacitor C is charged through R Soak time is typically one or two minutes, depending on the capacitor value. Next, the voltage source is turned off, and the capacitor is discharged through R sit for a few minutes with S

6514. Dielectric absorption is then calculated as follows:

% Dielectric Absorption = (Residual Voltage / Soak Voltage) × 100%

and S1 open (t3), and the residual voltage is then measured by Model

for the required soak time (t1 in Figure 3-9B).

(t2). The capacitor is allowed to

Figure 3-9

Measuring dielectric absorption

Volts and Ohms Measurements 3-15

6514

VOLTMETER

230

VOLTAGE SOURCE

A. Connections

Discharge

Soak Recovery

B. Voltage Waveform

Time

Amps Measurements

• Measurement overview — Summarizes the current measurement capabilities of Model

6514.

• Amps measurement procedure — Provides the procedure to measure amps.

• High-Impedance measurement techniques — Explains non-driven guarding tech-

niques to eliminate leakage currents in high-impedance test circuits.

• SCPI programming — Covers the basic SCPI commands used for the amps function.

• Amps measurement considerations — Covers measurement considerations that apply

to amps measurements.

• Applications — Covers applications to measure diode leakage current, capacitor leak-

age current, cable insulation resistance, and surface insulation resistance.

4-2 Amps Measurements

Measurement overview

Amps measurements — Model 6514 can make amps measurements from 100aA to 21mA

using 10 measurement ranges; 20pA, 200pA, 2nA, 20nA, 200nA, 2µA, 20µA, 200µA, 2mA, and 20mA.

External feedback — The external feedback mode of Model 6514 can be used to measure

logarithmic currents, and re-configure the input to use non decade current ranges. Measurements using the external feedback mode are covered in Section 11.

NOTE Accuracy specifications for all measurement functions are provided in Appendix A.

Amps measurement procedure

CAUTION The maximum input voltage and current to Model 6514 is 250V peak and

21mA. Exceeding either of these values may cause damage to the instrument that is not covered by the warranty.

WARNING The maximum common-mode input voltage, which is the voltage between

the input (HI or LO) and chassis ground, is 500V peak. Exceeding this value may create a shock hazard.

To achieve optimum precision for low-level current measurements, input bias current and voltage burden can be minimized by performing the offset correction procedures in Section 19. Information about these offsets are provided in “Current Measurement Considerations” (located in this section).

NOTE After measuring high voltage or high ohms, it may take several minutes for the input

current to drop to within specif ed limits. Input current can be verif ed by placing the protection cap on the input triax connector, and then installing the ground link between COMMON and CHASSIS ground. With the instrument on the 20pA range and zero check disabled, allow the reading to settle until the input bias current is within specif cations. The specifications for input bias current are listed in Appendix A.

Perform the following steps to measure current:

Step 1 Enable zero check and select the amps (I) function

The amps function is selected by pressing the I key.

Amps Measurements 4-3

Step 2 Perform zero correction

To achieve optimum accuracy for low current measurements, it is recommended that you zero correct the electrometer. To do so, select the 20pA range (which is the lowest range) and press the ZCOR key until the “ZZ” message is displayed. See Section 2 for details on zero correction.

Step 3 Select a manual measurement range or enable auto range

Step 4 Connect the current to be measured to the electrometer

Basic connections for amps measurements are shown in Figure 4-1.

NOTE Fundamental information on making connections to the electrometer input is pro-

vided in Section 2 (“Connection Fundamentals”).

WARNING A safety shield is required whenever a hazardous voltage (>30V) is present

on the noise shield. This can occur when the test circuit is ﬂoated above earth ground at a hazardous voltage level (see “Floating Measurements” in Section 2). Connections for the safety shield are shown in Figure 4-1. The metal safety shield must completely surround the noise shield or foating test circuit, and it must be connected to safety earth ground using #18 AWG or larger wire.

NOTE High-impedance current measurements require special measurement techniques.

These connection techniques are covered in “High-Impedance Measurement Techniques” (located in this section).

4-4 Amps Measurements

Figure 4-1

Connections for amps

237-ALG-2

Cable

Red (HI)

INPUT 250V PK

INPUT PREAMP

OFF

V, GUARD

(PROGRAMMABLE)

Green

(Chassis)

Black (LO)

PREAMP OUT

250V PK

GUARD

(FOLLOWS

INPUT)

(INTERNAL)

2V ANALOG

10K

OUTPUT

PREAMP

2V ANALOG

COM

COMMON CHASSIS

TRIGGER LINK

OUT

OUTPUT

6514 Rear Panel

LINE RATING

50, 60Hz

60 VA MAX

FUSE LINE

630mA

100 VAC

(SB)

120 VAC

220 VAC

315mAT

240 VAC

(SB)

Metal Noise Shield

Metal Safety Shield

Safety Earth Ground

RS232DIGITAL I/O

120

MADE IN

IEEE-488

(CHANGE IEEE ADDRESS

WITH FRONT PANEL MENU)

U.S.A.

Step 5 Disable zero check and take a reading from the display

filtering if the noise is caused by a noisy input signal and use damping if noise is caused by input capacitance. Filtering is covered in Section 6, and damping is discussed next.

Damping

uted to a long input cable or to the capacitance of the source, or a combination of both. Enabling damping will reduce this type of noise for current measurements. However, damping will also slow down the response of the measurement.

If the readings are noisy, you may want to use damping and/or f ltering to reduce noise. Use

High capacitance seen at the input will increase reading noise. This capacitance can be attrib-

Perform the following steps to enable or disable damping:

1. Press DAMP to display the present state of damping.

2. Use the

 or  key to display ON or OFF.

3. Press ENTER.

Amps Measurements 4-5

High impedance measurement techniques

Significant leakage could occur across a high impedance (≥1GΩ) DUT through the insulators as shown in Figure 4-3A where R ing just the current (I

) through R, you are also measuring the leakage current (IL). The current

measured by the ammeter is I

By connecting ammeter input LO to the metal mounting (guard) plate as shown in Figure 4-2B, the leakage current (I

ter. Therefore, the ammeter only measures I

and RL2 represent the leakage resistance. Instead of measur-

+ IL.

) is shunted to ammeter input LO and is not measured by the amme-

Figure 4-2

High impedance current measurements

A. Unguarded

*R = ≥1GΩ

Metal Mounting Plate

Metal Guard Plate

Insulators

IM = IR + I

6514

IM = I

B. Guarded

4-6 Amps Measurements

Floating current measurements — As discussed in Section 3 for volts measurements,

guarding uses a conductor at essentially the same potential as input HI to drastically reduce leakage currents in high-impedance test circuits. No current can f ow when there is a 0V drop across a leakage resistance.

For floating current measurements, ammeter input LO can be used as the guard since it totally surrounds input HI (via the input triax cable), and is at nearly the same potential as input HI. The actual voltage drop, known as voltage burden, depends on which measurement range is being used. The voltage burden values are listed in the specif cations (Appendix A).

Figure 4-3A shows an unguarded f oating current measurement in a high impedance circuit. The goal is to measure the current (I from ammeter input LO to test circuit common. Since the ammeter drops essentially 0V, approximately 10V is dropped by R (10V/1GΩ = 10nA). Therefore, the current that is measured by Model 6514 is the sum of the two currents (I = I corrupt the measurement.

Figure 4-3B shows the guarded version of the same circuit. Notice that the only difference is that the connections to the electrometer are reversed. Resistor R from ammeter input HI to ammeter input LO, and resistor R ter input LO (guard) to test circuit common. As previously mentioned, the ammeter drops almost 0V. If the actual voltage drop across the ammeter is <2mV, it then follows that there is a <2mV drop across R that is being measured by Model 6514 is the sum of the two currents (I = I of guarding reduced the leakage current from 10nA to <2pA. Note that the 10nA leakage current (I

) from ammeter input LO to test circuit common still exists, but it is of no consequence since

it is not measured by Model 6514.

) through resistor R. However, a leakage path (RL) exists

. The current through RL will be approximately 10nA

+10nA). Obviously, if IR is a low level current, then the 10nA leakage will

now represents the leakage

represents the leakage from amme-

. Therefore, the current through RL is <2pA (<2mV/1GΩ = <2pA). The current

+ <2pA). The use

Amps Measurements 4-7

Figure 4-3

Floating current measurements

10V

A. Unguarded

+10V

10V

+10V

6514

I = IR + 10nA

1GΩ

10V

1GΩ

= 10nA

6514

I = IR + <2pA

1GΩ

<2mV

IG =

1GΩ

10V

1GΩ

= <2pA

= 10nA

B. Guarded

4-8 Amps Measurements

SCPI programming

Table 4-1

SCPI commands — amps function

Commands Description Default Ref

[SENSe] SENSe Subystem:

:FUNCtion ‘CURrent’ Select Amps function. VOLT A :DATA? Return latest “raw” reading. B :CURRent

:DAMPing Enable or disable damping. OFF

INITiate Trigger one or more readings. B READ? Trigger and return reading(s). B

A) SENSe:FUNCtion <name>

Parameters ‘CURRent’ Amps function

‘VOLTage’ Volts function ‘RESistance’ Ohms function ‘CHARge’ Coulombs function

Note that the parameter names are enclosed in single quotes (‘). However, double quotes (“) can instead be used. Each measurement function “remembers” its own unique range setting.

B) SENSe:DATA?

To return a fresh (new) reading, you can send the INITiate command to trigger one or more readings before sending :DATA?. Details on INITiate are provided in Section 9.

While Model 6514 is busy performing measurements, the :DATA? command will not return the reading string until the instrument f nishes and goes into the idle state.

NOTES The format that the reading string is returned in is set by commands in the FORMat

Subsystem (see Section 16).

If there is no reading available when :DATA? is sent, an error (-230) will occur.

The READ? command can be used to return “fresh” readings. This command triggers and returns the readings. See Section 15 for details.

Programming example

The following command sequence will perform one zero corrected amps measurement:

*RST ‘ Return 6514 to RST defaults. SYST:ZCH ON ‘ Enable zero check. FUNC ‘CURR’ ‘ Select the Amps function. CURR:RANG 20e-12 ‘ Select the 20pA range. SYST:ZCOR ON ‘ Perform zero correction. CURR:RANG:AUTO ON ‘ Enable auto range. SYST:ZCH OFF ‘ Disable zero check. READ? ‘ Trigger and return one reading.

Amps measurement considerations

Amps Measurements 4-9

Some considerations for making accurate amps measurements are summarized as follows. Additional measurement considerations are covered in Appendix C. For comprehensive information on precision measurements, refer to the Low Level Measurements handbook, which is available from Keithley Instruments.

Input bias current

An ideal ammeter would read 0A with an open input. In practice, however, ammeters do have some current that f ows when the input is open. This current is known as the input bias (offset) current and may be large enough to corrupt low current measurements.

The input bias current for Model 6514 is listed in the specif cations. Input bias current may be reduced by performing the current offset correction procedure explained in Section 19.

Voltage burden

The input resistance of the ammeter causes a small voltage drop across the input terminals. This voltage is known as the voltage burden. If the voltage burden is large in relation to the voltage of the measured circuit, then signif cant measurement errors will occur.

Refer to Figure 4-4 to see how voltage burden affects current measurements. Assume V 5mV and R with zero voltage burden would measure the current source as follows:

is 5kΩ to configure a 1uA current source (5mV/5kΩ = 1µA). An ideal ammeter

------

5mV

------------ 1µA== =

5kΩ

4-10 Amps Measurements

In practice however, every ammeter has a voltage burden. If the voltage burden (VB) is 1mV,

the current will be measured as follows:

VSVB–

--------------------

The 1mV voltage burden caused a 20% measurement error. Percent error in a measured read-

ing (I

) due to voltage burden can be calculated as follows:

IM%error

The voltage burden of Model 6514 depends on the selected range (see specif cations). Voltage

burden may be reduced by performing the offset correction procedure in Section 19.

5mV 1mV–

------------------------------- 0.8µA== =

100%

---------------------=

()

S/VB

5kΩ

Figure 4-4

Voltage burden considerations

Noise

Source

VS - V

Meter

(Voltage

Burden)

Noise can seriously affect sensitive current measurements. The following paragraphs discuss

how source resistance and input capacitance affect noise performance.

Source resistance

The source resistance of the DUT will affect the noise performance of current measurements. As the source resistance is reduced, the noise gain of the ammeter will increase, as we will now discuss.

Figure 4-5 shows a simplif ed model of the feedback ammeter. R source resistance and source capacitance, V age. Finally, R

and CF are the feedback resistance and capacitance respectively.

is the source voltage, and V

The source noise gain of the circuit can be given by the following equation:

and CS represents the

is the noise volt-

NOISE

Output V

NOISE

Note that as R

Input V

decreases in value, the output noise increases. For example, when RF = RS,

NOISE

1 RF/R

+()=

the input noise is multiplied by a factor of two. Since decreasing the source resistance can have a detrimental effect on noise performance, there are usually minimum recommended source resistance values based on measurement range. Table 4-2 summarizes minimum recommended

Amps Measurements 4-11

source resistance values for various measurement ranges. Note that the recommended source resistance varies by measurement range because the R

value also depends on the measurement

range.

Table 4-2

Minimum recommended source resistance values

Minimum Recommended

Range

Source Resistance

pA 1GΩ to 100GΩ nA 1MΩ to 100MΩ µA 1kΩ to 100kΩ mA 1Ω to 100Ω

Figure 4-5

Source resistance and capacitance

Current Source

noise

Model 6514 Ammeter

4-12 Amps Measurements

Source capacitance

DUT source capacitance will also affect the noise performance of the Model 6514 ammeter. In general, as source capacitance increases, the noise also increases. To see how changes in source capacitance can affect noise gain, again refer to the simplif ed ammeter model in Figure 4-5. The elements of interest for this discussion are the capacitance, C itance C gain formula must be modif ed as follows:

. Taking into account the capacitive reactance of these two elements, the previous noise

and the feedback capac-

Output V

Here, Z

NOISE

represents the feedback impedance made up of CF and RF, while ZS is the source

impedance formed by R

-------------------------------------------------=

2πfRFC

()

Input V

NOISE

and CS. Furthermore,

1+[]

1ZF/Z

+()=

and,

-------------------------------------------------=

Note that as C Again, at the point where Z

The maximum value of source capacitance (C

2πfRSC

()

1+[]

increases in value, Z

= ZF, the input noise is amplif ed by a factor of two.

decreases in value, thereby increasing the noise gain.

) for Model 6514 ammeter is 10,000pF. You

can, however, usually measure at higher source capacitance values by inserting a resistor in series with the ammeter input, but remember that any series resistance will increase the voltage burden by a factor of I

IN RSERIES

. For example, the range of resistance listed in Table 4-2 will result in voltage burden values in range of 1mV to 1V. A useful alternative to a series resistor is a series diode, or two diodes in parallel back-to-back. The diodes can be small-signal types and should be in a light-tight enclosure.

Applications

The following applications require an external voltage source. The Keithley Model 230 volt-

age source is fully programmable and can source up to 100V at 100mA.

With the proper use of external triggering between Models 6514 and 230, the tests can be automated. All of the applications require a bias time or delay, which can be provided by the delay feature of Model 6514. When Model 6514 is triggered, a measurement will not be performed until the delay period expires.

NOTE External triggering and delay are covered in Section 9.

Diode leakage current

Figure 4-6 shows how to measure the leakage current for a diode. By sourcing a positive voltage, the leakage current through the diode will be measured. Note that if you source a negative voltage, you will forward bias the diode. Resistor R is used to limit current in the event that the diode shorts out or it becomes forward biased. Select a value of R that will limit current to 20mA or less.

A profile for leakage current can be developed by measuring current at various voltage levels. For example, you can program Model 230 to source from 1 to 10V in 1V steps. With the proper use of external triggering, Model 6514 will perform a current measurement on each voltage step. To ensure that the voltage is settled before each current measurement, you can program Model 6514 for a delay. For example, if you program Model 6514 for a one second delay, each measurement will be performed after the voltage step is allowed to settle for one second. The current measurements can be stored in the buffer.

Amps Measurements 4-13

Figure 4-6

Connections; diode leakage current test

NOTE Buffer operation is covered in Section 8.

Diode

230

V-Source

Equivalent Circuit

6514

Ammeter

4-14 Amps Measurements

Capacitor leakage current

Figure 4-7 shows how to measure the leakage current for a capacitor. The magnitude of the leakage is dependent on the type of dielectric and the applied voltage. A resistor and a diode are used to limit noise for the measurement.

For this test, a f xed bias voltage is to be applied to the capacitor for a specif ed time to allow the capacitor to fully charge (current decays exponentially with time). The leakage current is then measured. After the measurement, the voltage source is set to output 0V for a specif ed time to allow the capacitor to discharge.

Figure 4-7

Connections; capacitor leakage current test

V-Source

230

Equivalent Circuit

6514

Ammeter

Cable insulation resistance

NOTE For this test, Model 6514 uses the source voltage, measure current method to

insulator between the shield and the inner conductor is being measured. The cable sample should be kept as short as possible to minimize input capacitance to the ammeter.

the charging effects of cable capacitance to stabilize. The current is then measured. Cable resistance (R) can then be calculated as follows:

Figure 4-8

Connections; cable insulation resistance test

determine resistance. Once a current measurement is performed, resistance can be calculated.

Figure 4-8 shows how to measure the insulation resistance of a cable. The resistance of the

For this test a f xed bias voltage is applied across the insulator for a specif ed time to allow

R = V/I

where; V is the sourced bias voltage

I is the measured current

6514

Ammeter

230

V-Source

Cable

Resistance

Equivalent Circuit

Surface insulation resistance (SIR)

NOTE For this test, Model 6514 uses the source voltage, measure current method to

determine resistance. Once a current measurement is performed, resistance can be calculated.

Figure 4-9 shows how to measure the insulation resistance between PC board traces. Note that the drawing shows a "Y" test pattern for the measurement. This is a typical test pattern for SIR tests.

A bias voltage (typically 50V) is applied to the test pattern for a specif ed time (typically one second) to polarize the test pattern. The test voltage (typically 100V) is then applied and, after a specified time (typically one second), Model 6514 measures the current. Sur ace insulation resistance can now be calculated as follows:

SIR = V/I

where; V is the sourced test voltage

I is the measured current

Amps Measurements 4-15

Figure 4-9

Connections; surface insulation resistance test

230

V-Source

PC Board

Test Pattern

Equivalent Circuit

6514

Picommeter

Coulombs Measurements

• Measurement overview — Summarizes the charge measurement capabilities of the

Model 6514.

• Auto discharge — Explains how to use the auto discharge feature of Model 6514.

• Coulombs measurement procedure — Provides the procedure to measure coulombs.

• SCPI programming — Covers the basic SCPI commands used for the coulombs

function.

• Amps measurement considerations — Covers measurement considerations that apply

to coulombs measurements.

• Application — Summarizes an application to measure capacitance.

5-2 Coulombs Measurements

Measurement overview

Coulombs measurements — Model 6514 can make coulombs measurements from 10fC to

2.1µC using four measurement ranges; 20nC, 200nC, 2µC, and 20µC.

In the coulombs function, an accurately known capacitor is placed in the feedback loop of the amplifier so that the oltage developed is proportional to the integral of the input current in accordance with the following formula:

----

Where; V is the voltage

The voltage is scaled and displayed as charge.

External feedback — The external feedback mode of Model 6514 can be used to measure

non-standard charge ranges. Measurements using the external feedback mode are covered in Section 11.

NOTE Accuracy specifications for all measurement functions are provided in Appendix A.

Auto discharge

Model 6514 has an auto discharge feature for the coulombs function. When enabled, auto discharge resets the charge reading to zero when the specif ed charge level is reached. After the integrator resets, the charge measurement process simply restarts at zero. The charge reading resets every time the specif ed charge level is reached.

When auto discharge is disabled, you can use zero check to reset the integrator.

Perform the following steps to set an auto discharge level and enable it:

----==

itd

∫

C is the known capacitance Q is the charge

1. Press SHIFT and then AUTO-DIS to display the present auto discharge level.

2. Use the cursor keys ( ity, place the cursor on the “+” or “-” sign and press cursor on the range indicator and use the

3. With the desired auto discharge level displayed, press ENTER.

NOTE Pressing SHIFT and then AUTO-DIS a second time disables auto discharge

(“DISCHRG OFF” displayed brief y).

 and ) and (  and ) to enter a discharge level. To change polar-

 or . To change range, place the

 and  keys.

Coulombs measurement procedure

CAUTION The maximum input voltage and current to Model 6514 is 250V peak and

21mA. Exceeding either of these values may cause damage to the instrument that is not covered by the warranty.

WARNING The maximum common-mode input voltage, which is the voltage between

the input (HI or LO) and chassis ground, is 500V peak. Exceeding this value may create a shock hazard.

NOTE After measuring high voltage in the volts function, it may take several minutes for

input current to drop to within specif ed limits. Input current can be verif ed by placing the protection cap on the input triax connector, and then installing the ground link between COMMON and CHASSIS ground. With the instrument on the 20pA range and zero check disabled, allow the reading to settle until the input bias current is within specif cations. The specifications for input bias current are listed in Appendix A.

Perform the following steps to measure charge:

Step 1 Enable zero check and select the coulombs (Q) function

Coulombs Measurements 5-3

The coulombs function is selected by pressing the Q key.

Step 2 Select a manual measurement range or enable auto range.

Use the RANGE  and  keys to select a manual measurement range, or press AUTO to enable auto range. With auto range enabled, the instrument will auto range between the HIGH range group (2µC and 20µC) or the LO W range group (20nC and 200nC). To select the HIGH range group, press SHIFT and then the RANGE  key. To select the LOW range group, press SHIFT and then the RANGE  key. See Section 6 for details on range.

Step 3 If desired, set and enable auto discharge

See “Auto Discharge” to set an auto discharge level and enable it.

Step 4 Connect the input cable to Model 6514 (open input)

Make sure that the test circuit is not connected to the input.

Step 5 Disable zero check and press the REL key

When zero check is turned off, a charge may be induced on the input. Pressing the REL key zeroes the display. See “Zero Check Hop” in “Coulombs Measurement Considerations” (in this section). Details on Relative are provided in Section 7.

NOTE If the zeroed reading drifts signif cantly after REL is enabled, disable REL and toggle

zero check on and off until drift is minimized. Enable zero check and repeat Step 5.

5-4 Coulombs Measurements

Step 6 Connect the charge to be measured to the electrometer

Basic connections for amps measurements are shown in Figure 5-1.

NOTE See “Connection Basics” in Section 2 for fundamental information on making con-

nections to the electrometer input.

Figure 5-1

Typical connections for coulombs

Red (HI)

Metal Noise Shield

(Optional)

237-ALG-2

Cable

Black (LO)

Input LO connected to shield

INPUT 250V PK

INPUT PREAMP

OFF

V, GUARD

(PROGRAMMABLE)

PREAMP OUT

GUARD

(FOLLOWS

INPUT)

250V PK

(INTERNAL)

2V ANALOG

10K

OUTPUT

PREAMP

2V ANALOG

COM

COMMON CHASSIS

TRIGGER LINK

OUT

OUTPUT

LINE RATING

50, 60Hz

60 VA MAX

FUSE LINE

630mA

(SB)

315mAT

(SB)

100 VAC 120 VAC

220 VAC 240 VAC

RS232DIGITAL I/O

120

6514 Rear Panel

Step 7 Take the charge reading from the display

MADE IN

IEEE-488

(CHANGE IEEE ADDRESS

WITH FRONT PANEL MENU)

U.S.A.

If using auto discharge, use the REL key to zero the display when the integrator resets. Remember that Rel was enabled in Step 5. Therefore, you will have to press REL twice. The first press disables Rel, and the second press re-enables it to zero the display. See “Auto Discharge Hop” in “Coulombs Measurement Considerations” (in this section).

SCPI programming

Table 5-1

SCPI commands — coulombs function

Commands Description Default Ref

[SENSe] SENSe Subystem:

:FUNCtion ‘CHARge’ Select coulombs function. VOLT A :DATA? Return latest “raw” reading. B :CHARge

:ADIScharge Auto discharge:

[:STATe] Enable or disable auto discharge. OFF :LEVel <NRf> Set auto discharge level; -2.1e-5 to 2.1e-5. 2e-6

INITiate Trigger one or more readings. B READ? Trigger and return reading(s). B

Coulombs Measurements 5-5

A) SENSe:FUNCtion <name>

Parameters ‘CHARge’ Coulombs function

‘CURRent’ Amps function ‘VOLTage’ Volts function ‘RESistance’ Ohms function

Note that the parameter names are enclosed in single quotes (‘). However, double quotes (“)

can instead be used. Each measurement function “remembers” its own unique range setting.

B) SENSe:DATA?

To return a fresh (new) reading, you can send the INITiate command to trigger one or more readings before sending :DATA?. Details on INITiate are provided in Section 9.

While Model 6514 is busy performing measurements, the :DATA? command will not return the reading string until the instrument f nishes and goes into the idle state.

5-6 Coulombs Measurements

NOTES The format that the reading string is returned in is set by commands in the FORMat

Subsystem (see Section 16).

If there is no reading available when :DATA? is sent, an error (-230) will occur.

The READ? command can be used to return “fresh” readings. This command triggers and returns the readings. See Section 15 for details.

Programming example

The following command sequence will perform one coulombs measurement:

*RST ‘ Return 6514 to RST defaults. SYST:ZCH ON ‘ Enable zero check. FUNC ‘CHAR’ ‘ Select the Coulombs function. CHAR:RANG:AUTO ON ‘ Enable auto range.

SYST:ZCH OFF ‘ Disable zero check. CALC2:NULL:STAT ON ‘ Enable Rel to zero the display.

READ? ‘ Trigger and return one reading.

‘ Connect input cable.

‘ Connect charge circuit to DUT.

Coulombs measurement considerations

Some considerations for making accurate Coulombs measurements are summarized as follows. Additional measurement considerations are covered in Appendix C. For comprehensive information on precision measurements, refer to the Low Level Measurements handbook, which is available from Keithley Instruments.

Input bias current

A primary consideration when making charge measurements is the input bias (offset) current of the integrating amplif er. Any such current is integrated along with the input signal and reflected in the nal reading. Model 6514 has a maximum input bias of 4fA for charge at T (temperature at time of calibration). This input offset translates into a charge of 4fC per second at the T rect value.

Input bias current may be reduced by performing the offset correction procedure explained in Section 19.

temperature. This value must be subtracted from the f nal reading to obtain the cor-

CAL

External voltage source

When using an external voltage source, the input current should be limited to less than 1mA by placing a resistor in series with the high input lead. The value of this resistor should be at least:

R = 1000 × V (ohms)

where; V is the voltage across the resistor, or the compliance of the current being integrated.

CAL

Zero check hop and auto discharge hop

den change in the charge reading and is known as zero check hop. This sudden change in charge also occurs when the auto discharge feature resets the charge reading to zero. This hop in charge can be eliminated by taking a reading the instant zero check is disabled or when an auto discharge occurs, and subtracting it from all subsequent readings. A better way to deal with this hop in charge is to enable Rel immediately after zero check is disabled or when auto discharge resets the charge reading. This action nulls out the charge reading caused by the hop.

Application

Capacitance measurements

used to limit current. Select a value for R1 that will limit current to ≤100mA, and select a value for R2 that will limit current to ≤20mA.

waiting sufficient time for the capacitor to fully cha ge, open switch S1 and close switch S2 to measure the charge. The capacitance can now be calculated as follows:

Coulombs Measurements 5-7

Using the zero check feature (going from the enabled state to the disabled state) causes a sud-

Figure 5-2 shows a general test circuit to measure a capacitor (C). Resistors R1 and R2 are

When switch S1 is closed, the Keithley Model 230 voltage source charges the capacitor. After

Figure 5-2

Measuring capacitors

C = Q/V

where; C is the capacitance (in farads)

Q is the measured charge (in coulombs) V is the voltage used to charge the capacitor

S1 S2

R1 R2

230

V-Source

C = Q/V

6514

Range, Units,

Digits, Rate, and Filters

• Range, units, and digits — Provides details on measurement range, reading units, and

display resolution selection. Includes the SCPI commands for remote operation.

• Rate — Provides details on reading rate selection. Includes the SCPI commands for

remote operation.

• Filters — Explains how to configure and control the digital and median f lters. Includes

the SCPI commands for remote operation.

6-2 Range, Units, Digits, Rate, and Filters

Range, units, and digits

Range

The ranges for each measurement function are listed in Table 6-1. The range setting (f xed or AUTO) is remembered by each function.

Table 6-1

Measurement ranges

V I Ω Q

2V 20pA 2kΩ 20nC

20V 200pA 20kΩ 200nC

200V 2nA 200kΩ 2µC

20nA 2MΩ 20µC

200nA 20MΩ

2uA 200MΩ

20uA 2GΩ

200uA 20GΩ

2mA 200GΩ

20mA

The full scale readings for every measurement range are 5% over range. For example, on the 20V range, the maximum input voltage is ± 21V. Input values that exceed the maximum readings cause the overfl w message (“OVERFL0W”) to be displayed.

Manual ranging

To select a range, press the RANGE  or  key. The instrument changes one range per key-press. The selected range is displayed momentarily. If the instrument displays the “OVERFLOW” message on a particular range, select a higher range until an on-range reading is displayed. Use the lowest range possible without causing an overfl w to ensure best accuracy and resolution.

Autoranging

When using autorange, the instrument automatically goes to the most sensitive available range to measure the applied signal. Up-ranging occurs at 105% of range, while down-ranging occurs at the range value. For example, if on the 20V range, the instrument will go up to the 200V range when the input signal exceeds 21V. While on the 200V range, the instrument will go down to the 20V range when the input level goes to 20V.

The AUTO key toggles the instrument between manual ranging and autoranging. The AUTO annunciator turns on when autoranging is selected. To disable autoranging, press AUTO or the RANGE range.

 or  key. Pressing AUTO to disable autoranging leaves the instrument on the present

Range, Units, Digits, Rate, and Filters 6-3

Every time an autorange occurs, a search for every available range of the selected function is performed. The time it takes to perform the search could slow down range change speed significantly. For V, I and ( measurements, upper and/or lower autorange limits can be set to reduce search time. For Q measurements, the instrument will only autorange between the two higher charge ranges (high range group), or between the two lower charge ranges (low range group).

NOTE Range limits and groups are not in effect for manual ranging. Every range is accessi-

ble with manual range selection.

Autorange limits for V, I and Ω

Search time for V, I and Ω can be reduced by setting upper and/or lower autorange limits. For example, if you know the maximum input will be around 1µA, you can set the upper current range limit to 2µA. This eliminates the 20µA, 200µA, 2mA and 20mA ranges from the search, therefore, increasing the range change speed. Should the input exceed 2.1µA, the “OVERFLOW” message will be displayed.

Perform the following steps to set upper and/or lower autorange limits.

1. Select the V, I or Ω function.

2. Press SHIFT and then one of the following RANGE keys: a. Press the RANGE b. Press the RANGE

3. Use the RANGE

 key to display the present UPPER range limit.  key to display the present LOWER range limit.

 and  keys to display the desired limit.

4. Press ENTER.

NOTE If you attempt to select an incompatible range limit, it will be ignored and “TOO

LARGE” or “TOO SMALL” will be displayed brief y. For example, if the lower range limit is 20V, trying to set the upper limit to 2V will result in the “TOO SMALL” error.

Autorange groups for Q

To optimize range change speed for charge measurements, the instrument will only autorange between two ranges. With the high range group selected, the instrument can only autorange between the 2µC and 20µC ranges. With the low range group selected, the instrument can only autorange between the 20nC and 200nC ranges.

If the HIGH range group is presently selected and the instrument is on the 20nC or 200nC range (autorange disabled), pressing the AUTO range key will initially select the 2µA range and then enable autorange. If the range group is then changed to LOW, the instrument will initially go to the 200nC range with autorange enabled. Therefore, the instrument will always stay within the selected range group with autorange enabled.

NOTE With the low range group selected, the “OVERFLOW” message will be displayed

when the input signal exceeds 210nC.

Perform the following steps to select autorange group for Q:

1. Select the Q function.

2. Press Shift and then one of the follow RANGE keys: a. Press the RANGE b. Press the RANGE

 key to select the HIGH range group (2µC and 20µC).  key to select the LOW range group (20nC and 200nC).

6-4 Range, Units, Digits, Rate, and Filters

Units

Readings can be displayed using engineering (ENG) units (i.e. 1.236 MΩ) or scientif c (SCI)

notation (i.e. 1.236E+06Ω). Perform the following steps to change the units setting:

1. Press SHIFT and then DIGIT to display the present units setting (ENG or SCI).

2. Press the RANGE

3. Press ENTER.

NOTE 1. The units setting can only be changed from the front panel (no remote operation).

2. Scientific notation provides more resolution on small values than engineering units.

 or  key to display the desired units setting.

Digits

The DIGIT key sets display resolution for Model 6514. Display resolution can be set from 3½ to 6½ digits. This single global setting affects display resolution for all measurement functions.

To set display resolution, press (and release) the DIGIT key until the desired number of digits is displayed.

NOTE Changing the integration rate changes display resolution, but changing display reso-

lution does not change the rate setting (see RATE for details).

SCPI programming - range and digits

Table 6-2

SCPI commands — range and digits

Commands Description Default

For Range:

[:SENSe] SENSe Subsystem:

:VOLTage Measure voltage:

:RANGe Range selection:

[:UPPer] <n> Specify expected reading; -210 to 210 (V). 20V : AUTO Enable or disable autorange. (see Note)

:ULIMit <n> Specify upper range limit for autorange; -210 to 210 (V). 200V :LLIMit <n> Specify lower range limit for autorange; -210 to 210 (V). 2V

Range, Units, Digits, Rate, and Filters 6-5

Table 6-2 (cont.)

SCPI commands — range and digits

Commands Description Default

:CURRent Measure current:

:RANGe Range selection:

[:UPPer] <n> Specify expected reading; -0.021 to 0.021 (A). 200µA : AUTO Enable or disable autorange. (see Note)

:ULIMit <n> Specify upper range limit for autorange; -0.021 to 0.021 (A). 20mA :LLIMit <n> Specify lower range limit for autorange; -0.021 to 0.021 (A). 20pA

:RESistance Measure resistance:

:RANGe Range selection:

[:UPPer] <n> Specify expected reading; 0 to 2.1e11 (Ω). 200kΩ : AUTO Enable or disable autorange. (see Note)

:ULIMit <n> Specify upper range limit for autorange; 0 to 2.1e11 (Ω). 200GΩ :LLIMit <n> Specify lower range limit for autorange; 0 to 2.1e11 (Ω). 2kΩ

:CHARge Measure charge:

:RANGe Range selection:

[:UPPer] <n> Specify expected reading; -21e-6 to 21e-6 (C). 200nC : AUTO Enable or disable autorange. (see Note)

:LGRoup <name> Select autorange group; HIGH or LOW HIGH

For Digits:

DISPlay DISPlay Subsystem:

:DIGITs <n> Set display resolution; 4 to 7, where: 6

4 = 3½-digit resolution 5 = 4½-digit resolution 6 = 5½-digit resolution 7 = 6½-digit resolution

Note: Rational numbers can be used. For example, to set 4

resolution, send a value of 4.5 (the 6514 rounds it to 5).

Note: *RST default is ON and SYSTem:PRESet default is OFF.

Programming example — range and digits

The following command sequence selects the 200V range and sets display resolution to 3:

*RST ‘ Restore RST defaults. VOLT:RANG 200 ‘ Set V function to 200V range. DISP:DIG 3.5 ‘ Set display resolution to 3½ digits.

6-6 Range, Units, Digits, Rate, and Filters

Rate

The RATE key selects the integration time of the A/D converter. This is the period of time the input signal is measured. The integration time affects the amount of reading noise, as well as the ultimate reading rate of the instrument. The integration time is specif ed in parameters based on a number of power line cycles (NPLC), where 1 PLC for 60Hz is 16.67msec (1/60) and 1 PLC for 50Hz (and 400Hz) is 20msec (1/50).

In general, Model 6514 has a parabola-like shape for its speed vs. noise characteristics and is shown in Figure 6-1. Model 6514 is optimized for the 1 PLC to 10 PLC reading rate. At these speeds (lowest noise region in the graph), Model 6514 will make corrections for its own internal drift and still be fast enough to settle a step response <100ms.

Figure 6-1

Speed vs. noise characteristics

Voltage

Noise

Lowest

noise

region

166.7µs 16.67ms 166.67ms Integration Time

The rate setting is global for all measurement functions. Therefore, it does not matter what

function is presently selected when you set rate.

There are two ways to set rate. You can select slow, medium, or fast by using the RATE key, or you can set the number of power cycles from the NPLC menu that is accessed by pressing SHIFT and then NPLC.

Rate Key — The RATE key selections are explained as follows:

• SLOW — Selects the slowest front panel integration time (6 PLC for 60 Hz or 5 PLC for 50 Hz) and sets display resolution to 5½-digit resolution. The SLOW rate provides better noise performance at the expense of speed.

• MED — Selects the medium integration time (1 PLC) and sets display resolution to 5½-digit resolution. Select the MED rate when a compromise between noise performance and speed is acceptable.

•FAST — Selects the fastest front panel integration time (0.1 PLC) and sets display resolution to 4½-digit resolution. Select the FAST rate if speed is of primary importance (at the expense of increased reading noise).

To change the rate setting, press (and release) the RATE key until the desired rate annunciator

(SLOW, MED or FAST) is displayed.

Keithley Keithley Instruments 6514 Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

WARRANTY

Manual Print History

Table of Contents

List of Illustrations

List of T ables

Getting Started

General information

System electrometer features

Front and rear panel familiarization

Power-up

Display

Default settings

SCPI programming

Measurement Concepts

Measurement overview

Performance considerations

Connection fundamentals

Zero check and zero correct

Input bias current and offset voltage calibration

Measurement considerations

Measurement overview

Guarding

Volts and ohms measurement procedure

SCPI programming

Volts and ohms measurement considerations

Application

Amps Measurements

Measurement overview

Amps measurement procedure

High impedance measurement techniques

SCPI programming

Amps measurement considerations

Applications

Coulombs Measurements

Measurement overview

Auto discharge

Coulombs measurement procedure

SCPI programming

Application

Range, units, and digits

Rate